Fixing compaction crash by using executeQuery instead of executeUpdate
27705 read tests, compaction test, and few minor edits.

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: test
* Adds simple compaction test (testCompactSingleDoc).
Merge pull request #16 from cloudant/27705-read-tests

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