[Validator] do not assume specific of targets when building file_accessors to test against
[Validator] Added regression test for `undefined method `spec_consumer'`
[Validator] Improve file_accessor determination
[Validator] Improve regression test for `undefined method `spec_consumer'`

- let spec in "validates a podspec with dependencies" validate
- fixed a bug in `write_podspec`
Merge pull request #1130 from HBehrens/master

fix for erroneous linting on 0.21.0.rc1