Based on Brett's and Steve's feedback, I've pushed some tweaks to the captured git info.  With the changes, we now use --short form of git hash.  And we use output from "git describe --all --always --dirty" for the tag.  I added --all and --always for better results with development builds; the results should be the same for release (tagged) builds - I think.  I'm going to cherry pick this into 3.6.1 final and we can see how this works for development builds and further tweak as necessary.  Steve, note that I was brave and modified the Windows builds; yay, AppVeyor.  I'll also cherrypick these to 2.7 soon.

Expected outputs:
1. previous hg
2. previous git
3. updated git

Release (tagged) build:
1. Python 3.7.0a0 (v3.7.0a0:4def2a2901a5, ...
2. Python 3.7.0a0 (v3.7.0a0^0:05f53735c8912f8df1077e897f052571e13c3496, ...
3. Python 3.7.0a0 (v3.7.0a0:05f53735c8, ...

Development build:
1. Python 3.7.0a0 (default:41df79263a11, ...
2. Python 3.7.0a0 (master:05f53735c8912f8df1077e897f052571e13c3496, ...
3. Python 3.7.0a0 (heads/master-dirty:05f53735c8, ...

"dirty" means the working tree has uncommitted changes.
See "git help describe" for more info.