Integrated "memory broker" (membrk_t) abstraction.

Details:
- Integrated a patch originally authored and submitted by Ricardo Magana
  of HP Enterprise. The changeset inserts use of a new object type, membrk_t,
  (memory broker) that allows multiple sets of memory pools on, for example,
  separate NUMA nodes, each of which has a separate memory space.
- Added membrk field to cntx_t and defined corresponding accessor macros.
- Added membrk field to mem_t object and defined corresponding accessor macros.
- Created new bli_membrk.c file, which contains the new memory broker API,
  including:
    bli_membrk_init(), bli_membrk_finalize()
    bli_membrk_acquire_[mv](), bli_membrk_release(),
    bli_membrk_init_pools(), bli_membrk_reinit_pools(),
    bli_membrk_finalize_pools(),
    bli_membrk_pool_size()
- In bli_mem.c, changed function calls to
    bli_mem_init_pools()     -> bli_membrk_init()
    bli_mem_reinit_pools()   -> bli_membrk_reinit()
    bli_mem_finalize_pools() -> bli_membrk_finalize()
- In bli_packv_init.c, bli_packm_init.c, changed function calls to:
    bli_mem_acquire_[mv]() -> bli_membrk_acquire_[mv]()
    bli_mem_release()      -> bli_membrk_release()
- Added bli_mutex.c and related files to frame/thread. These files define
  abstract mutexes (locks) and corresponding APIs for pthreads, openmp, or
  single-threaded execution. This new API is employed within functions
  such as bli_membrk_acquire_[mv]() and bli_membrk_release().

frame/thread/bli_thread.h

@@ -5,6 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
+   Copyright (C) 2016 Hewlett Packard Enterprise Development LP
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are
@@ -51,6 +52,9 @@
   #define BLIS_ENABLE_MULTITHREADING
 #endif
 
+// Include thread mutex (mtx_t) object definitions and prototypes.
+#include "bli_mutex.h"
+
 // Include thread communicator (thrcomm_t) object definitions and prototypes.
 #include "bli_thrcomm.h"