Fix Core#188 : pod search now uses plain-text + new optional `--regex` flag

[Integration] Fix issue when a build configuration contains a slash

Fixes #2767

Change default to use ARC and specify on per file basis if it's disabled.

CLANG_ENABLE_OBJC_ARC='NO' on a project basis with -fobjc-arc for each
file to enable ARC on a project basis with CLANG_ENABLE_OBJC_ARC='YES' and using -fno-objc-arc for each file in pods that don't require ARC

Fixes #2803

[Resolver] Show a helpful error message if the old resolver incorrectly activated a   pre-release version that now leads to a version conflict

[Resolver] Show a helpful error message if the old resolver incorrectly activated a   pre-release version that now leads to a version conflict

Closes #2759

Fix :head pods

[Rakefile] Remove old references to compiling Xcodeproj

[IntegrationSpec] Compare execution_output.txt

[Resolver] Fix crash when there are lockfile dependencies that were never actually installed (i.e. incompatible platform subspecs)

See https://github.com/CocoaPods/CocoaPods/issues/2789#issuecomment-61797151.