Style & spec updates (rev 2)

No functional changes beyond those

Revised to satisfying a few missing style constraints
Add '~> 2.0' specifier to rspec dev dependency

RSpec 3 (just released) changes 'truthiness' expectations API.

Restricts rspec to 2.x until rspec 3.x support is more widespread
Merge pull request #93 from ManageIQ/rspec2

Add '~> 2.0' specifier to rspec dev dependency
Merge pull request #90 from ManageIQ/style_n_specs

Style & spec updates
Expand doc files list / matchers
Add Gem#file_name helper
Update metadata during distgit update process
Prefix %gem_instdir to non-special files in String#rpmize

Few additional style changes / cleanups to rpmize / unrpmize
Merge pull request #94 from ManageIQ/rpmize_prefix

Prefix %gem_instdir to non-special files in String#rpmize
Merge pull request #97 from ManageIQ/distgit_metadata

Update metadata during distgit update process
Merge pull request #95 from ManageIQ/file_name

Add Gem#file_name helper
Merge pull request #96 from ManageIQ/doc_files

Expand doc files list / matchers
Expand polisher errors, raise errors on various edge cases  (rev 3)

Some refactoring including expansion of ConfHelpers module
and reorganizing Polisher::Gem#versions. Specs added to test
the later (and gem_dependency_checker verified)

Revised to rebase against master again