gtg broken when installed in /usr/local

The data directory is chosen in GTG/__init__.py

LOCAL_ROOTDIR = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
DIST_ROOTDIR = "/usr/share/gtg"
 [...]
#GTG directories setup
if not os.path.isdir( os.path.join(LOCAL_ROOTDIR,'data') ) :
    DATA_DIR = DIST_ROOTDIR
else:
    DATA_DIR = os.path.join(LOCAL_ROOTDIR,'data')

Therefore, DATA_DIR cannot be /usr/local/share/gtg, which is the default data directory if gtg is installed via "python setup.py install".
 If that is done, gtg will output several errors due to missing files in /usr/share (e.g.
 Failed to open file '/usr/share/gtg/icons/hicolor/16x16/apps/rtm_image.png': No such file or directory)