Add checks in mem_pool to catch possible double frees
Add checks in mem_pool to catch possible double frees

Signed-off-by: shishir gowda <shishirng@gluster.com>
Signed-off-by: Vijay Bellur <vijay@dev.gluster.com>

BUG: 1520 (gnfs crashes on start-up in mem_get0)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=1520

Kaushikbv/Gluster,Kaushikbv/Gluster,Kaushikbv/Gluster