[SourcesManager] More robust generation of source names from URLs
[SourcesManager] Fix the handling of invalid URLs
[Validator] Allow the validator to take specific sources

Allows customizable source for `pod spec lint` and `pod lib lint`, with both defaulting to `master`.
Ignore 'InputFile' errors from xcodebuild.
Added a unittest for the InputFile filtering.
[Validator] take URLs instead of actual sources
Merge pull request #2566 from CocoaPods/validator-sources

[Validator] Allow the validator to take specific sources
[Outdated] Take into account the sources specified in Podfile