fcl-db: memds: implemented Locate and Lookup methods for TMemDataset.
(some inspiration and ideas taken from TDBF)
+ TestLookup
Bug #9614

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25946 3ad0048d-3df7-0310-abae-a5850022a9f2