Andres Kroonmaa's MemPool tidyup, take 1. Take a whole bunch of

Andres Kroonmaa's MemPool tidyup, take 1. Take a whole bunch of
xmalloc/xcalloc's and replace them with mempool'ed versions of
things. Not everything has been converted, but this is a start.
Notable weirdnesses are:

* aufs - there are now a few pools which are used for string allocation
  for things like object paths. This might not be the most optimal
  solution but its better than what existed.

* pconn.c - an initial pconn FD set is mempool'ed, and if the pconn set
  grows bigger than PCONN_FD_SZ it changes to xmalloc()

* client_side.c - the incoming request buffer is now initially mempooled,
  of size CLIENT_REQ_BUF_SZ (4096 bytes atm). If it needs to grow, it
  changes to xmalloc()