27705 read tests, 28325 fix TD_Database -compact: crash, and few minor edits.

This adds a set of READ tests to the Tests project. Related to these READ tests, TD_Database+Insertion -compact: was crashing due to incorrect FMDB call. There were a few other minor changes.

READ tests:
* Adds testGetNonExistingDocument
* Adds READ after compaction test (testGetCompactedDocumentRev)
  
Minor edits:  
* Adds test to delete document with old revision in testDeleteDocument
* Properly sets NSError* to nil
* Removes pointless testForSqlTables

TD_Database -compact: crass
* Fixes TD_Database+Insertion compact: crash -- use FMDatabase executeQuery
instead of executeUpdate:
* Adds simple compaction test (testCompactSingleDoc).