Fix package_name and final_dmg inconsistency if safe name != name

If the project name has characters such as "-" in, package_name wasn't
resolving to what was created in the final output. This fix ties the two functions
together to avoid that, and also work with other packagers than "pkg".
Make dmg compressor package_name def more readable
Remove the dmg compressor final_dmg def
Add unit spec coverage for packager affecting dmg compressor package_name.

The original specified behaviour has changed as well, no longer containing
the name/version/build iteration behaviour in the dmg, so it's spec is updated
to show that.
Simplify dmg package path using base package_path
Fix #366 (Arch Linux `truncate_platform_version': undefined method `split' for nil:NilClass (NoMethodError)).
Update test for platform_version in metadata to check for 'rolling' as /etc/arch-release no longer contains a version hint (deprecated some time ago).
rolling, rolling.
Merge pull request #367 from flaccid/archlinux_platform_version

Fix #366 Arch Linux does not have major and minor release numbers
Merge pull request #358 from andytson/feature/fix-dmg-pkg-missmatch

Fix package_name and final_dmg inconsistency if safe name != name
Change `makeself` package extension back to `.sh`

This follows the convention used by most all self-extracting shaballs 
for the last 25 years. If you doubt that go talk to @lamont-granquist 
and he’ll set you on the correct path.
Merge pull request #370 from opscode/schisamo/fix-makeself-extension

Change `makeself` package extension back to `.sh`
More aix awesomeness
Rebasing