fixes osx bug where user couldn't change proxy or connect to network

by default osx passes a -psn arg when launching an app from command
line. this is a process serial number argument and py2app when used with
emulate_argv=True removes it.
commit d2097c15d9 removed this, thus
introducing the -psn arg on launch. this is misinterpreted by the arg
parser as a proxy setting, breaking networking.

electrum

@@ -189,6 +189,10 @@ def run_command(cmd, password=None, args=None):
 
 if __name__ == '__main__':
 
+    #on osx, delete Process Serial Number arg generated for apps launched in Finder
+    if is_bundle == 'macosx_app' and sys.argv[1][:4] == '-psn':
+        del sys.argv[1]
+
     wallet = None
     parser = arg_parser()
     options, args = parser.parse_args()