Fix total lines for multi-repository stats.

Make general stats total LOC show the total aggregate from all projects,
instead of the total LOC from last project.

[hoxu@users.sf.net: rewrote the commit message]

Signed-off-by: Heikki Hokkanen <hoxu@users.sf.net>

gitstats

@@ -517,7 +517,7 @@ class GitDataCollector(DataCollector):
 					print 'Warning: failed to handle line "%s"' % line
 					(files, inserted, deleted) = (0, 0, 0)
 				#self.changes_by_date[stamp] = { 'files': files, 'ins': inserted, 'del': deleted }
-		self.total_lines = total_lines
+		self.total_lines += total_lines
 
 		# Per-author statistics