Fix resource allocation problems:
Fix resource allocation problems:

- Completely recoded the ypmatch cache code. The old code could leak
  memory: it would allow the cache to grow, but never
  shrink. The new code imposes the following limits:

	o The cache is capped at a limit of 5 entries.
	o Each entry expires after five seconds, at which point
	  its slot is freed.
	o If an insertion is to be done and all five slots
	  are filled, the oldest entry is forcibly expired
	  to release its slot.

  Also, the cache is implemented on a per-binding basis rather than
  having a global cache covering all bindings. This means that each
  bound domain has its own 5 slot cache.

- Changed clntudp_create() to clntudp_bufcreate() so that the
  xmit/recv message buffer sizes can be set explicitly. NIS transactions
  are rarely much larger than 1024 bytes since YPMAXRECORD is 1024.
  The defaults chosen by clntudb_create() are actually much larger
  than needed. I set the xmit buffer to a little over 1024 and the
  recv buffer to a little over 2048. This saves a few Kbytes for each
  NIS binding.

- Add my name to the copyright. I think I've made enough changes to
  this file to merit it. :)

Note: these changes should go into the 2.2.x branch, but I'm waiting
on feedback from a tester to see if the cache fixes solve the reported
memory leak problem.

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