Standard_Failure now holds an optional stack trace dump.
Added function Standard::StackTrace() dumping backtrace to the string.
SegvHandler within OSD_signal now appends backtrace to the message
if OSD::SignalStackTraceLength() is set to non-zero value
or environment variable "CSF_DEBUG_MODE" is set for debugging.
Added auxiliary macros Standard_NOINLINE disallowing function inlining.
Command "dsetsignal" has been extended by -strackTraceLength argument
for defining stack trace length within signals redirected to C++ exceptions.
Added "ddebugtraces" command for debugging purposes (adding stack traces to all exceptions).
