Handle HG:Extra lines in commit parsing

There is a chance that a commit has N number of HG: lines in a commit.

see: https://github.com/mozilla/addon-sdk

This will filter those lines out so parsing still works

src/commit.coffee

@@ -89,6 +89,12 @@ module.exports = class Commit
       while /^kilnhgcopies/.test lines[0]
         lines.shift()
 
+      # if converted from mercurial gpgsig may be present with non-valid gpg lines
+      # e.g. "HG:extra rebase_source:6c01d74dd05f50ede33608fe3f1b2049d93abbda"
+      # and  "HG:rename-source hg"
+      while /^HG:/.test lines[0]
+        lines.shift()
+
       # not doing anything with this yet, but it's sometimes there
       if /^encoding/.test lines[0]
         encoding = _.last lines.shift().split(" ")