Use better formula to determine local GAE environment

Author: zacbir

click/_compat.py

@@ -8,7 +8,9 @@
 
 PY2 = sys.version_info[0] == 2
 CYGWIN = sys.platform.startswith('cygwin')
-APP_ENGINE = os.environ.get('SERVER_SOFTWARE', '').startswith('Development')
+# Determine local App Engine environment, per Google's own suggestion
+APP_ENGINE = ('APPENGINE_RUNTIME' in os.environ and
+              'Development/' in os.environ['SERVER_SOFTWARE'])
 WIN = sys.platform.startswith('win') and not APP_ENGINE
 DEFAULT_COLUMNS = 80