Updated CHANGELOG for Core/pull/84

Thanks @dlackty

Conflicts:
	lib/cocoapods/generator/xcconfig/aggregate_xcconfig.rb
	spec/unit/generator/xcconfig/aggregate_xcconfig_spec.rb

Try to fix spec failure on master

Updated CHANGELOG for #1978

* 'master' of https://github.com/apalancat/CocoaPods:
  Test and documentation for issue #1694
  Unset the `CDPATH` env variable before shelling-out. #1694

Conflicts:
	CHANGELOG.md

Make SourcesManager ignore some global git configs

Update changelog for #1704, #1840 & #1933

Merge branch 'fix_head_download_option' of https://github.com/neonichu/CocoaPods into neonichu-fix_head_download_option

Conflicts:
	spec/unit/installer/pod_source_installer_spec.rb

Updated CHANGELOG for #1958

Added changelog entry for pull #1960

Cleanup pod directory when download fails (probably due to a network error)

Conflicts:
	CHANGELOG.md

Fixes #1950.