Compiled PHP process functions missing writeMessageEnd()

While testing a PHP implementation of TJSONProtocol, we noticed that the process_* functions created by

thrift -r --gen php:server

were missing a call to

$output->writeMessageEnd();

This probably went unnoticed in testing to this point because TBinaryProtocol.php does not issue a message end marker. But with JSON, the message needs to be closed with a closing square bracket.

The attached patch adds the message end call.

Generated code has been tested with ThriftTest.thrift and TBinaryProtocol, as well as with our new JSON implementation.