Store full gem dependency during gemfile analysis
Add some utility helpers to git modules

Git::Repo#include? indicates if file is in repo
Git::Pkg#spec? indicates if distgit pkg has spec
Git::Pkg#valid_targets returns valid configured branches
Add TagMapper utility to associate distgit/koji tags together
Implement Gem#state and Gemfile#dependency_states (rev 2)

Infers state of gem and gems in gemfile from various targets
in distgit/koji build process.

Revised to incorporate alternate workflow. A little less efficient
(for example distgit repo/branch will always be checked even
 if build exists but doesn't match) but code is alot cleaner

Manually verified, specs still TBD
Merge pull request #100 from ManageIQ/gem_state

Fix #91: Implement Gem#state