wsgicgi: call close() on iterable to avoid resource leaks

Quoting PEP 333 (WSGI):

"If the iterable returned by the application has a close() method, the server
or gateway must call that method upon completion of the current request,
whether the request was completed normally, or terminated early due to
an error. (This is to support resource release by the application.
This protocol is intended to complement PEP 325's generator support,
and other common iterables with close() methods."

mercurial/hgweb/wsgicgi.py

@@ -69,5 +69,9 b' def launch(application):'
         return write
 
     content = application(environ, start_response)
-    for chunk in content:
-        write(chunk)
+    try:
+        for chunk in content:
+            write(chunk)
+    finally:
+        if hasattr(content, 'close'):
+            content.close()