padre hangs when debugger is launched

Steps to reproduce:

  1. save the initial empty file
  2. click the "Launch debugger" button

`padre` never returns and needs to be killed with SIGTERM. Right after the GUI appears it prints `17:55:19: Debug: Failed to connect to session manager: SESSION_MANAGER environment variable not defined` to console.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: padre 1.00+dfsg-3
Uname: Linux 4.1.1-040101-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.17.2-0ubuntu1.1
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Jul 2 17:53:56 2015
InstallationDate: Installed on 2015-06-08 (24 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: padre
UpgradeStatus: Upgraded to vivid on 2015-06-09 (23 days ago)