Fix resource bundles for not build targets

Conflicts:
	spec/cocoapods-integration-specs

Conflicts:
	spec/cocoapods-integration-specs
	spec/integration.rb

This can been skipped for not-build targets. In addition, there needs to
be a target dependency from the aggregate target to the resource bundle
target so that it is actually getting built.

[Source Manager] Fix issue with source without URL

Added a spec which tests installation of resources.

Closes #2965

Do not rely on ~/.cocoapods being present.

directory.

Closes https://github.com/CocoaPods/CocoaPods/issues/2859.

[ExternalSource] Store downloaded external source podspecs as JSON, evaluated from the context of the source directory

[Changelog] Add entry for external source podspecs being evaluated in the source directory and stored as JSON

[ExternalSource] Store downloaded external source podspecs as JSON, evaluated from the context of the source directory

Do not generate targets for Pods without sources

Thanks @segiddins.

If a PodTarget should not be build:
- Do not install a target
- Skip the non-existing native targets in Installer
- Do not add linker flags to XCConfig

Validate that a specification's `public_header_files` and `private_header_files` file patterns only match header files.

Validate that a specification's `public_header_files` and `private_header_files` file patterns only match header files.
Also, validate that all file patterns, if given, match at least one file.