kill all aspects related to masks in the tracing interface

details:
- TRACE_start (filename) and TRACE_start_with_mask (filename, mask)
are replaced by TRACE_start, which takes tracing configurations
from the xbt_cfg_set, defined in the file instr_config.c
- new TRACE_start must be called after MSG_global_init, in
order to have the proper configurations defined

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@8110 48e7efb5-ca39-0410-a469-dd3cf9ba447f