linuxhooking: fix calloc crash and prevent recursion

On Ubuntu 12.04 Precise the calloc hooking crashes. So let's
implement it more the way like it is described here:
http://www.slideshare.net/tetsu.koba/tips-of-malloc-free

It requires the recursion prevention mechanism. So we can call e.g.
malloc within the malloc hook with this.
discovery: simplify ptr-to-heap discovery

The little helpers for auto-completing the libmemdisc config should
be available for ptr-to-heap discovery as well. So rework and unify
this handling.
examples: warzone2100: update ptrmem sizes