CocoaPods v0.39.0 errors with Facebook SDK v4.7 - swift2

Question

Old Cocoapods Configuration
I am using Xcode 7 Beta 4. Initially I was using Cocoapods version 0.38.2 and when I ran pod install --verbose in Terminal it said it downloaded dependencies for Bolts, FBSDKCoreKit, FBSDKLoginKit, FBSDKShareKit, FBSDKMessengerShareKit, and Pods for iOS 8.1. With this setup my app compiled successfully. Below is the Podfile and Objective-C Bridging File that I used to import the Facebook SDK (so Swift recognises its referenced methods and Objective-C classes). Note that the specific versions shown in my Podfile are also the versions that get installed even if I do not explicitly specify them at the time of this writing.
Podfile
xcodeproj '/Users/<my_username>/MyApp/MyApp.xcodeproj'
pod "FBSDKCoreKit", "~> 4.7.0";
pod "FBSDKLoginKit", "~> 4.7.0";
pod "FBSDKShareKit", "~> 4.7.0";
pod "FBSDKMessengerShareKit", "~> 1.3.1";
MyAppObjCBridging.h
#ifndef MyAppObjCBridging_h
#define MyAppObjCBridging_h
#import <FBSDKCoreKit/FBSDKCoreKit.h>
#import <FBSDKLoginKit/FBSDKLoginKit.h>
#import <FBSDKMessengerShareKit/FBSDKMessengerShareKit.h>
#import <FBSDKShareKit/FBSDKShareKit.h>
#endif
Problems encountered when updating to Cocoapods v0.39.0 (from v0.38.2)
The console showed the message "CocoaPods 0.39.0 is available. To update use: gem install cocoapods. Until we reach version 1.0 the features of CocoaPods can and will change. We strongly recommend that you use the latest version at all times.", so I installed the this latest version of Cocoapods 0.39.0 by executing sudo gem install cocoapods in Terminal.
But when I compiled my app it gave me the following errors:
/Users//MyApp/MyApp/MyAppObjCBridging.h:14:9: 'FBSDKCoreKit/FBSDKCoreKit.h' file not found
In Xcode I "Product > Clean" (CMD+SHIFT+K), but this did not make any difference. So I ran sudo gem uninstall cocoapods in Terminal (which listed 0.38.2 and 0.39.0 as the versions that were currently installed) and selected version 0.39.0 from the list to uninstall the latest version and revert back to 0.38.2. I then ran pod install --verbose. When I tried to compile my app it compiled successfully and ran in Simulator again.
Question 1
Why does it give the error that it can't find "FBSDKCoreKit/FBSDKCoreKit.h" when I use Cocoapods version 0.39.0 instead of the older version 0.38.2?
Question 2
If when using Cocoapods version 0.38.2 (the version that compiles with my app) I decided to add platform :ios, '9.0' to the first line of my Podfile (above its existing contents) and run pod install --verbose in Terminal, the Terminal messages tell me that it installs each pod target for iOS 9.0 (instead of iOS 8.1) (i.e. - Installing targetFBSDKCoreKitiOS 9.0).
When I then run my app it successfully compiles and opens in Simulator and displays some new warnings associated with iOS9, most of which I understand. However I do not understand why this one appears. Why is this warning appearing?:
ld: warning: directory not found for option '-L/Users/Ls/code/swift/FreeWifiSearch/FreeWifiSearch/build/Debug-iphoneos'
Question 3
When using Cocoapods version 0.38.2 (the version that compiles with my app), if I decided to add use_frameworks! to the first line of my Podfile, and platform :ios, '9.0' to the second line of my Podfile (above its existing contents), and then run pod install --verbose in Terminal, the Terminal messages tell me that it installs each pod target for iOS 9.0 (instead of iOS 8.1).
When I then run my app the following errors appear:
Use of unresolved identifier 'FBSDKLoginButton'
Use of unresolved identifier 'FBSDKLoginManager'
Use of unresolved identifier 'FBSDKLoginBehaviour'
Why does adding use_frameworks! to the top of my Podfile prevent me from using the Facebook SDK identifiers? (noting that when I don't have use_frameworks! at the top of my Podfile my app successfully compiles and runs in Xcode Simulator, and I can successfully retrieve a Facebook SDK Access Token and login to Facebook)

Answer 1

Since posting the original questions the following was performed and resulted in no compiler errors:
Updated from Xcode 7 Beta 4 to Xcode 7.1.1 by downloading latest from App Store
Added use_frameworks! and platform :ios, '9.0' to top of Podfile
Changed deployment target to iOS 9.0: Project Settings > Targets > General > Deployment Info > Deployment Target > 9.0
Updated CocoaPods to v0.39 with sudo gem install cocoapods
Reinstalled pods with pod update --verbose
Added import FBSDKLoginKit above the class containing Facebook SDK methods
Performed Clean (Shift+CMD+K) and Run (CMD+R) in Xcode to test on device

Answer 2

Add "${PODS_ROOT}/Headers/Public/FBSDKCoreKit/FBSDKCoreKit" in your target's Header Search Paths in Build Settings
For me it's OK now(CocoaPods 0.39, FBSDK 4.10)