Added memory corruption checks to stacktrace.c

Added memory corruption checks to stacktrace.c

The stacktrace now produces backtraces using backtrace().

The stacktrace now supports basic memory corruption checks in
addition of memory leak checks.  It supports double free checks,
invalid free checks and out of bound checks.

Environment variables SILC_MALLOC_NO_FREE and SILC_MALLOC_DUMP
can be used to get even more information out of it.