Enable stacktrace logging by default

[Castaglia]

Currently, ProFTPD has some support for logging stacktraces in e.g. the face of a SIGSEGV signal -- but only if the --enable-devel=stacktrace compile-time option is used. Those stacktrace logging can be very useful when diagnosing errors, and especially when users report errors. That being the case, why not have stacktrace support enabled by default, rather than disabled by default? There would then be a --disable-stacktrace compile-time option offered, of course.

Note that in order for stacktrace logging to work, the installed binaries must not be stripped. Thus when working on this feature, make sure to adjust the Makefiles' install targets accordingly.

[Castaglia]

There are some other considerations that affect stack traces to be researched: compiler optimization flags, suid restrictions, etc.

[Castaglia]

I'd like to get this enhancement into 1.3.6, in order to support #254 . Specifically, I'd like to include stack traces in the logged errors, when necessary. See also this pull request.

[Castaglia]

From the glibc manual on backtraces, it looks like we'll need to add the -rdynamic linker flag, at the very least.

[Castaglia]

Fixed in master.