Mulgara, allocateDirect, swap space

On sequences of large Mulgara queries, Java was crashing for lack of swap space. Culprit appears to be the lack of reuse of ByteBuffers, all of which are direct byte buffers (and thus outside heap space).

First crack was using pojo byte buffers (fixed swap issue). Second was/is making some of the read only and one-at-a-time classes reuse their buffers by adding a Block recycling method.

edit: Reusing buffers in the find method cuts the live memory for my test "large" searches by a tick over 40%, according to HPROF. Response time for the servlet is decreased as well, but the proportion varies from 40% to 25% according (I suspect) to how big a slice the IO accounts for.