Allow leading spaces in http() requests

zope.app.testing.functional.HTTPCaller allowed you to write

    >>> print http(r"""
    ... GET / HTTP/1.1
    ... Headers: headers etc.
    ... """)

I don't see why zope.app.wsgi.testlayer.http() can't do the same.

This makes porting large ancient test suites easier.

src/zope/app/wsgi/testlayer.py

@@ -208,7 +208,7 @@ def __str__(self):
 
 
 def http(wsgi_app, string, handle_errors=True):
-    request = TestRequest.from_file(BytesIO(string))
+    request = TestRequest.from_file(BytesIO(string.lstrip()))
     request.environ['wsgi.handleErrors'] = handle_errors
     response = request.get_response(wsgi_app)
     return FakeResponse(response)