Revert "MINOR: threads: change lock_t to an unsigned int"

This reverts commit 8f1f177ed0bbdb6c10e61e83994df113452d434f.

Repeated tests have shown a small perforamnce degradation of ~1.8%
caused by this patch at high request rates on 16 threads. The exact
cause is not yet perfectly known but it probably stems in slower
accesses for non-64-bit aligned atomic accesses.
1 file changed