s4: some additional out of memory checks for the python auth bindings

[Matthias Dieter Wallnöfer]

Andrew,

could you please review the topmost patches in my "master" branch? 
Really interesting I find the current behaviour in "py_lp_ctx_new". Do 
we really need two memory contexts or does my patch work which converts 
this to only use one (this has been discovered by running "provision" 
under valgrind)?

Cheers,
Matthias