Gperf fix

Since gperf was slow, better replace it with a slow to call solution at runtime but fast to generate, it's not like we'll be generating stacktraces often in the life cycle of a program.

Surprisingly enough, even on nitg, the stacktrace does not take long to generate, which is a good thing.

For comparison :

~~~
$ time nitg nitg.nit --stacktrace libunwind
user	0m19.720s

$ time nitg nitg.nit --stacktrace nitstack
user	0m19.820s
~~~

At the same time, a bug was introduced by myself earlier on in sockets, a commit is here to fix that.