Include strings.h for strcascmp() (win32 breakage)

Change-Id: Ic29ed91564310da4a9dd72d5a40a1368c115fccf
Reviewed-on: http://review.couchbase.org/42830
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>