Remove $GITCMD variable

After commit c5d159c $GITCMD is only used once, so 'inline it', which also allows us to get rid of the 'eval' call.
rev-parse git command doesn't need the --work-tree argument

small tidyup
Status message updates

Make it clearer that "modules" actually means "kernel modules", and display a message while extracting tarball (which can take a while).
Merge pull request #112 from lurch/patch-4

Remove $GITCMD variable
Merge pull request #113 from lurch/patch-5

Status message updates