Fix the way the segments are included in the gcore outputs (with the

Fix the way the segments are included in the gcore outputs (with the
default invokation):
- Right now if segments are not writable are not included. Remove this.
- Right now if a segment is mapped with NOCORE the check is not honoured.
  Change this by checking the newly added flag, from libutil,
  KVME_FLAG_NOCOREDUMP.

Besides that, add a new flag (-f) that forces a 'full' dump of all the
segments excluding just the malformed ones. This might be used very
carefully as, among the reported segments, there could be memory
mapped areas that could be vital to program execution.

Sponsored by:	Sandvine Incorporated
Discussed with:	kib
Reviewed by:	emaste
Tested by:	Sandvine Incorporated
MFC after:	2 weeks