[gemspec] Bump xcodeproj to 0.19.3

Fixes #2631.
[Analyzer] Ensure external sources are downloaded when needed

Closes https://github.com/CocoaPods/CocoaPods/issues/2494.
[Integration] Fix integration while project is open

While a user project is open and we delete/change the xcconfig files which
the user project references. It causes any subsequent builds to fail
until the project is closed/re-opened, or the project file is touched.

This commit touches the file if we do not need to save it, thus causing
Xcode to reload it.

Closes #2627
Closes #2665
[Gemspec] Bump to Xcodeproj 0.19.4
[Gemspec] Bump to cocoapods-trunk 0.3.1
Indentation! Indentation! Indentation!

Indentation! Indentation! Indentation! Indentation! Indentation!
[ErrorReport] Include git information in stack

Closes https://github.com/CocoaPods/CocoaPods/issues/2678.
[LICENSE] Time. It still passes.
Added a mising backtick in xcconfig_integrator warning message
fixes crash when using file URLs https://github.com/CocoaPods/CocoaPods/issues/2683
Merge pull request #2686 from nemesis/add-a-missing-backtick

Added a mising backtick in xcconfig_integrator warning message
added spaces in CHANGELOG and reversed conditional in name_for_url method
Merge pull request #2687 from Kurry/2683-crash-when-using-file-url

fixes crash when using file URLs.
Fixes usage of pods in static libraries with Xcode 6.

Fixes #2666.
Merge pull request #2676 from CocoaPods/issue/2666

Fixes an issue when using pods in static library targets
Update spec integration fixtures
[Resources] Fix when Xcode is installed with space in path

Fixes #2684
Update spec integration fixtures
[travis] Simplify configuration and use bundler cache
[Spec] Fix stubbing removed method resulting in test taking 10s