Fix `pod install` failure on `platform :ios`
ReactiveCocoa v2.1 is still compatible with iOS 5.0 and OS X 10.7
Revert indent change

caused by the commit: 7622ccefa14456fc9e2875b8deda7ee5ca61118a
Revert changes to `s.prepare_command`

caused by the commit: f51915f79e15516e0e581a91275ab7bfebde1cc9

These renamings are needed to avoid conflict with some specs, e.g. 'Mantle'.
See https://github.com/CocoaPods/Specs/commit/3a8c0e23a13f98857b8c6c8ae8ca8c69b95df362 .
DTrace source files are automatically processed by Xcode
RACExtensions doesn't exist anymore

https://github.com/ReactiveCocoa/ReactiveCocoa/pull/817
Merge pull request #4379 from ikesyo/fix-reactivecocoa-2_1

Fix ReactiveCocoa v2.1 podspec