[fortran, patch] Allow displaying backtraces from user code

[Tobias Burnus]

Janus Weil wrote:
>>> >>So, in principle I'm fine with all your BACKTRACE_* variants (except
>>> >>for _splurge, maybe;)
>>> >>
>>> >>Or, why not just (plain and simple) "BACKTRACE"?
>> >The name is the same as backtrace() in glibc, but otherwise, sure why
>> >not. _show/_print might be preferable in the sense that they convey
>> >that stuff will be directly printed on the screen, rather than, say,
>> >the procedure returning an array of strings with the stack trace info.
> Agreed. Let's go with BACKTRACE_SHOW.

I have to admit that I prefer show_backtrace to backtrace_show, which 
sounds a bit clumsy. I also don't think that finding show_backtrace is 
more difficult than finding backtrace_show. "backtrace" is in the index, 
looking at the documentation, one can still search for "backtrace" and 
search engines should find "backtrace" in either way. (A name which 
comes just into my mind is: "backtrace_now()"; I am not claiming that it 
is better than any of the others.)

Enough of bikeshadding: I think having the possibility to simply print a 
backtrace is very useful! Hence, I leave the name to Janus and Janne.

Tobias