encryption/crypt: Add mem-accounting for crypt xlator

Without these changes crypt.t crashes when compiled with -DDEBUG

Change-Id: I1f7372aa30a09dbe3ae81d1dd598cf36e17fe0b7
BUG: 1030058
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/7319
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>