Allow the specification of custom container types in Thrift IDL files

Allow the specification of custom container types in Thrift IDL files

Summary: If you want your map to be a hash_map instead of an stl::map, we now have a directive in Thrift to let you do that.

Instead of:
map<i32,i32>

You can do:
map[cpp:hash_map<int32_t,int32_t>]<i32,i32>

This tells the Thrift compiler to explicitly use whatever type was specified in the brackets when generating C++ code, instead of the implied Thrift type.

Reviewed By: aditya

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@664828 13f79535-47bb-0310-9956-ffa450edef68