Fix podspec in Podfile with no options.

Added specs to test podspec method inside Podfile. Specs for the
default, no options version; the :name version and the :path
version.
Merge pull request #768 from drodriguez/gh-708-podspec-nil-options

Fix podspec in Podfile with no options.
Generate Pods target in Mac OS X with the specified deployment target.

Fix #757