Create gdp-version.txt while creating gdp-version.sh for use in simple
places like Makefiles.
Attempt to do a better job getting the git information into the binary
--- it failed to recreate git-version.txt in some circumstances, even
though the code had been changed.
Try to carry git version information over to builds that have no .git
subtree (as might happen if you use rsync).
Avoid error message when compiled without git tree available.
Put git commit id into generated binaries.