[libvirt] [PATCH 0/2] Make a wrapper for fork()

This was partly prompted by DV's suggestion last week. The first of these patches creates a new function called virFork() which behaves (almost) like fork() but takes care of some important details that pretty much any call to fork() should be doing. The 2nd switches three fork-calling functions in util.c over to using virFork() instead of fork(). In the future, except for odd circumstances, code that needs to fork should call virFork() instead, and if there is anything determined to be universally necessary at fork-time, it should be added to virFork() rather than to the callers of virFork(); hopefully this will ease maintenance and reduce replicated bugs. (Note that, while this is just an overall "code health" patch, a couple bug fix patches I'll be submitting either tomorrow or Thursday will assume it as a prerequisite).