ckeck GISBASE

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@38400 15284696-431f-4ddb-bdfa-cd5b030d7da7

scripts/g.extension/g.extension.py

@@ -129,7 +129,7 @@ def cleanup():
     grass.try_rmdir(tmpdir)
 
 def install_extension(svnurl, prefix, module):
-    gisbase = os.environ['GISBASE']
+    gisbase = os.getenv('GISBASE')
     if not gisbase:
         grass.fatal('$GISBASE not defined')