Handle anonyous function

In case of an anonymous function (which is named __lambda_func
internally by PHP), we leave early in get_frame_context.
Extract filename / lineno in case of anonymous functions.

In the case of an anonymous function, the filename is sent as:
"</path/to/filename>(<lineno>) : runtime-created function"
We do the proper extraction.
Merge pull request #137 from llange/runtime_created_function

Runtime created function