Standardize on install_dir

Sorry for the confusion folks, but it seems like the move to install_path was
an unwise one. It is impossible to retain backwards compatability using
install_path, and all the other methods in omnibus use the "_dir" suffix,
especially those in the Config object.

This commit is basically a revert of c4c604b, but has some additional fixes
thus making it not a real "revert".
Expose Software#dependencies as part of the public DSL API
Expose Project#dependencies as part of the public DSL API
Rename install_path_cache_dir to git_cache_dir

The naming of this method is super confusing to new users. We should call it
what it is - the git_caching dir.
Remove Mixlib::Config. Evaluate Config in a cleanroom.
Object#remove_instance_variable is private in Ruby 1.9
Add the ability to disable git caching
Remove platform and platform version from package names for
el, freebsd, windows, and other.
* Add architcture to solaris/aix/freebsd package names.
* Deprecation notice for #iteration in favor of #build_iteration.
Use #build_iteration instead of (deprecated) #iteration.
Update tests to use #build_iteration.
Remove unneeded quotes.
Use pkgmk_version for the version string of a package built with pkgmk.
Extract makeself build into its own packager.
Unit tests for makeself packager.