init: probe if sqlite works

Help the user get annex.dbdir configured when their filesystem is not
one that sqlite works on.

The change in Database.Handle makes an error from sqlite not be ignored
besides being displayed, which it was before. I can't see any reason
git-annex would want to ignore these errors.

I chose to use the fsck database rather than the keys database because
opening the keys database populates it, and see commit
b3c4579c79.

The placement of the call to checkSqliteWorks inside checkInitializeAllowed
avoids annex.uuid getting set before it's called.

Sponsored-by: Dartmouth College's Datalad project

Database/Handle.hs

@@ -123,7 +123,7 @@ workerThread db tablename jobs = newconn
 	newconn = do
 		v <- tryNonAsync (runSqliteRobustly tablename db loop)
 		case v of
-			Left e -> hPutStrLn stderr $
+			Left e -> giveup $
 				"sqlite worker thread crashed: " ++ show e
 			Right cont -> cont