Fixme; check .git/HEAD's mtime as well.
Add 'dont_cache' option to always build; use it for llvm.

Conflicts:
	packages/mono-llvm.py
Make GitHubPackage check whether the revision has changed.

We now write the current git revision into build-root/<package>.revision
and force a rebuild if it has changed.

Also removed the two hacks from my previous commits.

Conflicts:
	packages/mono-llvm.py
Oops, also call the base class'es method.
Disable compile warnings to make this build with Xcode5.
Move to packaging using pkgbuild/productbuild.

We're now using the new packaging toolchain so that we can start
code-signing the installers.

This commit also reformatted the file to adhere to pep8 coding
standards.

Conflicts:
	profiles/mono-mac-release/mono-mac-release.py
Fix up cwd and path to resources in run_pkgbuild.