Fixed wrong computation of start timer.
cleanup, use C99
do not make irverify code dependent on NDEBUG
remove verification sflag
rework verify code

The new code has less options and variants, if you call irg_verify()
verification is performed, regardless of DEBUG_libfirm, or NDEBUG being
set and regardless of firm verification setting switches. On the other
side no atomic dump and abort is performed anymore, the call has to do
this, though an irg_assert_verify() function has been added as a
convenience measure.
There has also been a complete rewrite of the actual checking performed.
The new code is simpler, should produce more consistent output and
can report more than one error.