Fixed --browser behaviour when --server-name provided

Fixed PR Pylons#1533. Calling:
   pserve --server-name abc --browser app.ini
caused error : "LookupError: No section 'main' (prefixed by 'server') found in config app.ini"

pyramid/scripts/pserve.py

@@ -9,7 +9,7 @@
 # lib/site.py
 
 import atexit
-import ctypes
+import ctypes.
 import errno
 import logging
 import optparse
@@ -391,7 +391,7 @@ def serve():
 
         if self.options.browser:
             def open_browser():
-                context = loadcontext(SERVER, app_spec, name=app_name, relative_to=base,
+                context = loadcontext(SERVER, app_spec, name=server_name, relative_to=base,
                         global_conf=vars)
                 url = 'http://127.0.0.1:{port}/'.format(**context.config())
                 time.sleep(1)