Fix the trylock call, it returns 0 when the mutex is acquired.
Add information about Linux performance tuning to our docs.

Specifically reference transparent huge pages and NUMA zone
reclamation.
Fix compiler warning:

In file included from ../src/include/wt_internal.h:258,
                 from ../src/block/block_addr.c:8:
../src/include/btree.i: In function '__wt_page_modify_init':
../src/include/btree.i:253: warning: implicit conversion shortens 64-bit
value into a 32-bit value