Various upgrades, with the effect that mozilla now runs, although

Various upgrades, with the effect that mozilla now runs, although
it has tremendous performance problems.

* Implement pthread_key_{create,delete} and pthread_{set,get}specific.

* Implement pthread_cond_timedwait.  A nuisance.

* New timer infrastructure, based on the RDTSC instruction.  This
  allows fast, accurate time measurement without swamping the host with
  gettimeofday() syscalls.

There's something definitely screwy about the scheduler, making opera
run slowly and mozilla run unbelievably slowly.  To be investigated.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@119