Also adds unit tests for the SSSDConfig API

This should fix #218
It should also prevent us from leaking memory in case the original request times
out and should prevent races with the callbacks beeing freed after sdp_req is
freed and thus dereferencing freed memory in the callbacks detructors.

Always use the network timeout defined in the options.
But raise defaults to 60 seconds or enumerations can easily fail.

Loop control variable was not being incremented.
I also converted a goto loop into a do...while loop to make it
easier to follow the logic.

Update gettext strings

- this fixes a compiler warning about the redefinition of
  SIZEOF_OFF_T in the python bindings, because python is
  compiled with large file support.

Timers always come before fd events, wait 5 microseconds between processing
operations so that tevent has a chance of cactching an fd event in between.
This allows the backend to reply to pings even while processing very large ldap
results (importanty especially during the first enumeration).