Fix memory LIKE & bugfix in mongo

b9d5daf fixes a bug that could be exploited like the included test case demonstrates.

7a60fca copies the regex constructing stuff into the memory adapter. I repeated myself as I'm unsure if that code belongs in utilities or geddy. Maybe a `utils.string.like2regex`?

Tests still fail, but I'm pretty sure it's #69 that's doing this. Looking into that now.