Remove libextobjc submodule
Read part of libextobjc into the ReactiveCocoa folder as a subtree
Re-add jspahrsummers/xcconfigs into the external/ folder
Fix up libextobjc and xcconfig project file references
Replace EXTScope cleanup with namespaced static inline

This avoids symbol conflicts if EXTScope.m is included via two
different projects.
Namespace the rest of EXTScope for consistency
Remove .gitmodules entry for libextobjc
++xcconfigs to project-headers-first
++xcconfigs
++xcconfigs
Go back to quoted imports for RAC

This way, imports from within the project will use the USER_HEADER_SEARCH_PATHS setting, and not end up with the headers from the build folder.
Move the contents of RACBacktrace+Private into the prefix header

Importing a header from the prefix header seems to use different search paths, so this is safer for avoiding conflicts.
Fix up RACBacktraceSpec
Merge branch '2.0-development' into libextobjc-subtree

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa/UIBarButtonItem+RACCommandSupport.m
	ReactiveCocoaFramework/ReactiveCocoa/UIButton+RACCommandSupport.m
Merge pull request #612 from ReactiveCocoa/libextobjc-subtree

Replace libextobjc submodule with a subtree