Handle special files and frames in python stacktraces

Note: special_function and special_file sound quite weird but I wasn't able to
come up with better alternative (unnamed_function?). Let me know if you can
think of something better.

--->8--->8--->8--->8--->8--->8--->8--->8--->8--->8--->8--->8---

Python code can be executed from stdin or from string (in case of eval
and similar functions), and python stack frames need not come from named
functions but can also be contained in lambdas and module-level code.

This patch:
- Adds special_file and special_function booleans to the python frame
  structure and its python object counterpart. These are true when the
  above mentioned conditions occur.
- Changes the JSON format so that the python frame contains e.g.
  special_function: "module" key-value pair for module level functions
  instead of function_name: "xyz" which is used for ordinary functions.
  Special files are treated in similar way.

Closes #74.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Signed-off-by: Richard Marko <rmarko@redhat.com>