Add memory pool locking functions

Add memory pool locking functions

Adding debuging functionality to lock and unlock memory pool.

2 ways to debug code:
crc - is default checksum/hash of the locked pool.
      It gets slower when the pool is larger - so the check is only
      made when VG is finaly released and it has been used more then
      once.Thus the result is rather informative.

mprotect - quite fast all the time - but requires more memory and
           currently it is using posix_memalign() - this could be
	   later modified to use dm_malloc() and align internally.
           Tool segfaults when locked memory is modified and core
	   could be examined for faulty code section (backtrace).

Only fast memory pools could use mprotect for now -
so such debug builds cannot be combined with DEBUG_POOL.