prepare 0.15 release

ChangeLog

-Gajim 0.15 (XX XX 2012)
+Gajim 0.15 (18 March 2012)
 
   * Plugin system
   * Whiteboard (via a plugin)

autogen.sh

 #!/usr/bin/env bash
-  gajimversion="0.15-beta4"
+  gajimversion="0.15"
   if [ -d ".hg" ]; then
     node=$(hg  tip --template "{node}")
     hgversion="-${node:0:12}"

src/common/defs.py

@@ -27,7 +27,7 @@
 basedir   = '../'
 localedir = '../po'
 
-version = '0.15-beta4'
+version = '0.15'
 import subprocess
 try:
     node = subprocess.Popen('hg tip --template "{node|short}"', shell=True,