Fix install for OS X

OS X uses BSD tar which does not know -a (Archive) option.
Seems like GNU tar doesn't really need it too.

qake shell script was assuming the newly installed make-4.0
is in the path. Changed to explicitly use the path of the installed
binary (saved in qake/.make_path during installation)
Selects either md5 or md5sum automatically

md5 is used in BSD derived systems (OS X, FreeBSD, etc.)
Merge pull request #4 from nimrody/osx

Implement better OS X support