[Darwin/macosx] Add support for the optional :clang argument
(cherry picked from commit 2dadabebee3a43c02b5cd53cc06e00ca81d00d19)

From: Conrad Kramer <conrad@kramerapps.com>

git-svn-id: http://svn.howett.net/svn/theos/trunk@604 4410221e-0ddf-4ce3-99c0-2db6c0dbc727
[logos] Check for group nonexistence BEFORE trying to set custom class initializers.

From: Dustin L. Howett <dustin@howett.net>

git-svn-id: http://svn.howett.net/svn/theos/trunk@605 4410221e-0ddf-4ce3-99c0-2db6c0dbc727
[common] control and layout/ are no longer mutually exclusive. ./control takes precedence over ./layout/DEBIAN/control.

From: Dustin L. Howett <dustin@howett.net>

git-svn-id: http://svn.howett.net/svn/theos/trunk@606 4410221e-0ddf-4ce3-99c0-2db6c0dbc727
Merge remote-tracking branch 'upstream/master'
Cleanup temporary .deb packages that weren't built with FINALPACKAGE=