Make the C# generator use non-hardcoded namespaces.

Make the C# generator use non-hardcoded namespaces.

- Make the C# generator use program->get_namespace("csharp")
  instead of program->get_csharp_namespace()
- Eliminate the explicit "csharp_namespace" in t_program.
- Deprecate the csharp_namespace token.
- Update example .thrift files and syntax files.

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665611 13f79535-47bb-0310-9956-ffa450edef68