Free SnapshotMarkers

> ::findleaks
BYTES             LEAKED         VMEM_SEG CALLER
12288                 12 fffffd7ffc35f000 MMAP
12288                  1 fffffd7ffcf7c000 MMAP
8192                   1 fffffd7ffcf6d000 MMAP
12288                  1 fffffd7ffcd7d000 MMAP
12288                  1 fffffd7ffcd6d000 MMAP
8192                   1 fffffd7ffc96d000 MMAP
12288                  1 fffffd7ffc95c000 MMAP
8192                   1 fffffd7ffc76e000 MMAP
12288                  1 fffffd7ffc75d000 MMAP
8192                   1 fffffd7ffc56f000 MMAP
12288                  1 fffffd7ffc55e000 MMAP
12288                  1 fffffd7ffc36f000 MMAP
------------------------------------------------------------------------
           Total      12 oversized leaks, 131072 bytes

CACHE             LEAKED           BUFCTL CALLER
0000000000485028       1 00000000089eb2a0 ep.so`MemoryTracker::MemoryTracker+0x6b
000000000048a028     512 0000000008a6cb60 libstdc++.so.6.0.17`operator new+0x1e
------------------------------------------------------------------------
           Total     513 buffers, 32776 bytes
> 0000000008a6cb60::bu
bufctl
bufctl_audit
> 0000000008a6cb60::bufctl -v
            ADDR          BUFADDR        TIMESTAMP           THREAD
                            CACHE          LASTLOG         CONTENTS
         8a6cb60          8a6b880    c3fb052e883da                5
                           48a028                0                0
                 libumem.so.1`umem_cache_alloc_debug+0xfd
                 libumem.so.1`umem_cache_alloc+0xb3
                 libumem.so.1`umem_alloc+0x64
                 libumem.so.1`malloc+0x3f
                 libstdc++.so.6.0.17`operator new+0x1e
                 ep.so`UprConsumer::snapshotMarker+0xc7
                 ep.so`EvpUprSnapshotMarker+0x75
                 bucket_engine.so`upr_snapshot_marker+0x8a
                 upr_snapshot_marker_executor+0x100
                 process_bin_packet+0xb8
                 complete_nread+0x182
                 conn_nread+0x48
                 event_handler+0x1ce
                 libevent_core-2.0.so.5.1.9`event_base_loop+0x436
                 worker_libevent+0x56

Change-Id: I8aeafa031b6fd9ae5d918abd9820558b311a9a72
Reviewed-on: http://review.couchbase.org/38664
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>