hg-to-git: fix parent analysis

Fix a bug in the hg-to-git convertor introduced by commit
1bc7c13: when searching the changeset
parents, 'hg log' returns an extra space at the end of the line, which
confuses the .split(' ') based tokenizer:

    Traceback (most recent call last):
      File "hg-to-git.py", line 123, in <module>
          hgchildren[mparent] += ( str(cset), )
      KeyError: ''

Signed-off-by: Stelian Pop <stelian@popies.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/hg-to-git/hg-to-git.py

@@ -111,7 +111,7 @@ def getgitenv(user, date):
 hgbranch["0"] = "master"
 for cset in range(1, int(tip) + 1):
     hgchildren[str(cset)] = ()
-    prnts = os.popen('hg log -r %d --template "{parents}"' % cset).read().split(' ')
+    prnts = os.popen('hg log -r %d --template "{parents}"' % cset).read().strip().split(' ')
     prnts = map(lambda x: x[:x.find(':')], prnts)
     if prnts[0] != '':
         parent = prnts[0].strip()