PHP Generator: Throw an exception on bad types.

PHP Generator: Throw an exception on bad types.

Summary:
Previously, if you set a structure field to, say, an int when it was
supposed to be a container (array) or struct (object), the serialization
code would either produce corrupt output (container) or cause a fatal
error (struct).  Now they both throw exceptions.

Reviewed By: mcslee

Test Plan: Looked at generated code.

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@666365 13f79535-47bb-0310-9956-ffa450edef68