prepare beta3 release

autogen.sh

 #!/usr/bin/env bash
-  gajimversion="0.15-beta2"
+  gajimversion="0.15-beta3"
   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-beta2'
+version = '0.15-beta3'
 import subprocess
 try:
     node = subprocess.Popen('hg tip --template "{node|short}"', shell=True,