grass.py: clarify error message from https://trac.osgeo.org/grass/changeset/59210

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@59216 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/init/grass.py

@@ -1238,7 +1238,8 @@ cygwin = "cygwin" in sys.platform
 macosx = "darwin" in sys.platform
 
 if 'GISBASE' in os.environ:
-    sys.exit(_("ERROR: GRASS GIS seems to be already running. Exiting."))
+    sys.exit(_("ERROR: GRASS GIS is already running "
+               "(environmental variable GISBASE found)"))
 
 # Set GISBASE
 os.environ['GISBASE'] = gisbase