setup: read .hg_archival.txt for version info (issue1670)

Previously, setup.py was enhanced to identify the Mercurial version
from either .hg/ or mercurial/__version__.py. When archives are
created using 'hg archive' or via hgweb, neither of those options are
available. However, there is a .hg_archival.txt file in the root of
the archive that has the information. This patch enhances setup.py to
identify the Mercurial version from the .hg_archival.txt file when
there is no .hg/ or mercurial/__version__.py available.

setup.py

@@ -97,6 +97,8 b' try:'
 except ImportError:
     pass
 
+version = None
+
 if os.path.isdir('.hg'):
     # execute hg out of this directory with a custom environment which
     # includes the pure Python modules in mercurial/pure
@@ -105,7 +107,6 b" if os.path.isdir('.hg'):"
     os.environ['PYTHONPATH'] = os.pathsep.join(['mercurial', purepath, pypath])
     os.environ['HGRCPATH'] = '' # do not read any config file
     cmd = [sys.executable, 'hg', 'id', '-i', '-t']
-    version = None
 
     l, e = subprocess.Popen(cmd, stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE).communicate()
@@ -122,6 +123,12 b" if os.path.isdir('.hg'):"
             version = l[-1] # latest tag or revision number
             if version.endswith('+'):
                 version += time.strftime('%Y%m%d')
+elif os.path.exists('.hg_archival.txt'):
+    hgarchival = open('.hg_archival.txt')
+    for line in hgarchival:
+        if line.startswith('node:'):
+            version = line.split(':')[1].strip()[:12]
+            break
 
     if version:
         f = file("mercurial/__version__.py", "w")
@@ -129,6 +136,7 b" if os.path.isdir('.hg'):"
         f.write('version = "%s"\n' % version)
         f.close()
 
+
 try:
     from mercurial import __version__
     version = __version__.version