Multiple Directory Conversion

Multiple Directory Conversion

Code added/modified to merge and convert many CTF binary files located
in different directories into one ASCII file.

Edit by Mathieu Desnoyers:

- Introduce struct trace_collection, because this will eventually be
  seen as an API to the outside world, so I want to hide the internal
  dependency on glib types.
- Added #define _XOPEN_SOURCE 700 needed for openat and nftw at the top
  of babeltrace.c.

Signed-off-by: Amer Alhalabi <amer.alhalabi@ericsson.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>