Fix buffer overflow bug in StringCompare()

Includes benchmark for comparing different StringCompare() implementations.

Change-Id: Ib4623b3ae6c99977af332ce5161da66af3cae9e5
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2168
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: Skye Wanderman-Milne <skye@cloudera.com>