ck_rwlock: Re-observe latch bits if necessary.
ck_rwlock: Acquire semantics for ordering on  latch bits.
ck_rwlock: Add ck_rwlock_read_latchlock operation.

This avoids degradation on read_lock path for use-cases not
requiring latch semantics.
ck_rwlock: Ignore latch bits on write lock operation.
ck_rwlock: Re-organization of write-side operations and latch support for write_trylock.
ck_rwlock: Additional re-organization of write-side functions.
ck_rwlock: Additional reorganization.
regressions: Benchmark coverage for latchlock operations.