Extract exact version from a tagged git archive.

Produce exact version with GitHub zip archives from the releases/tags page.
No need to upload sdist archives anymore.

Author: pavoljuhas

Diff for: diffpy/Structure/gitarchive.cfg

@@ -2,3 +2,4 @@
 commit = $Format:%H$
 date = $Format:%ai$
 timestamp = $Format:%at$
+refnames = $Format:%D$

Diff for: setup.py

@@ -32,6 +32,7 @@ def gitinfo():
 
 
 def getversioncfg():
+    import re
     from ConfigParser import RawConfigParser
     vd0 = dict(version=FALLBACK_VERSION, commit='', date='', timestamp=0)
     # first fetch data from gitarchivecfgfile, ignore if it is unexpanded
@@ -40,6 +41,9 @@ def getversioncfg():
     cp0.read(gitarchivecfgfile)
     if '$Format:' not in cp0.get('DEFAULT', 'commit'):
         g = cp0.defaults()
+        mx = re.search(r'\btag: v(\d[^,]*)', g.pop('refnames'))
+        if mx:
+            g['version'] = mx.group(1)
     # then try to obtain version data from git.
     gitdir = os.path.join(MYDIR, '.git')
     if os.path.exists(gitdir) or 'GIT_DIR' in os.environ: