convert/gnuarch: parse continuation-of revisions in gnuarch source

In GNU Arch, continuation-of was often used for:
 - tagging revisions
 - continue working on a project in a new archive, because arch
   was scaling poorly in revision numbers (cat-logs were slow
   to be parsed and scanned through)
 - very similar to the previous point, fork his own branch of
   a project.

Parsing this header information will allow to 'follow' new history
because it often hints at older/forked/personal revision trees.

This patch however just implements the parsing of the
continuation-of header. A followup patch will implement the proper
use of this new information.

hgext/convert/gnuarch.py

@@ -14,6 +14,7 b' class gnuarch_source(converter_source, c'
             self.summary = ''
             self.date = None
             self.author = ''
+            self.continuationof = None
             self.add_files = []
             self.mod_files = []
             self.del_files = []
@@ -239,6 +240,8 b' class gnuarch_source(converter_source, c'
                              '%Y-%m-%d %H:%M:%S'))
             self.changes[rev].author = catlog['Creator']
             self.changes[rev].summary = catlog['Summary']
+            if catlog.has_key('Continuation-of'):
+                self.changes[rev].continuationof = catlog['Continuation-of']
 	except Exception, err:
             raise util.Abort(_('could not parse cat-log of %s') % rev)