`spack -V` previously always returned the version of spack from
`spack.spack_version`. This gives us a general idea of what version
users are on, but if they're on `develop` or on some branch, we have to
ask more questions.
This PR makes `spack -V` check whether this instance of Spack is a git
repository, and if it is, it appends useful information from `git
describe --tags` to the version. Specifically, it adds:
- number of commits since the last release tag
- abbreviated (but unique) commit hash
So, if you're on `develop` you might get something like this:
$ spack -V
0.13.3-912-3519a1762
This means you're on commit 3519a1762, which is 912 commits ahead of
the 0.13.3 release.
If you are on a release branch, or if you are using a tarball of Spack,
you'll get the usual `spack.spack_version`:
$ spack -V
0.13.3
This should help when asking users what version they are on, since a lot
of people use the `develop` branch.
c029c8ff89