Unprotected updates to ut_total_allocated_memory in
os_mem_alloc_large() and os_mem_free_large(), called during
fast index creation, may corrupt the variable and cause assertion failures.

Also, add UNIV_MEM_ALLOC() and UNIV_MEM_FREE() instrumentation around
os_mem_alloc_large() and os_mem_free_large(), so that Valgrind can
detect more errors.

rb://90 approved by Heikki Tuuri.  This addresses Issue #177.