play could be more restrictive about combinations that make no sense

[alexlehm]

Framework version: play 1.1rc3, gae-head
Platform you're using: windows xp, java 1.6.0-22

Reproduction steps:

I spent a while trying to track down an error 500 on GAE, which in the end was an option I had still in the conf file for a normal database integration (db=mem).
This means that play tries to initialize a database which causes a security error on google, but it works in dev mode since there is no security restriction.
I think it would be better to have deploy or even the run command fail when the combination of features doesn't make sense or will not work.

Something similar happened before when I had an @entity annotation still in the model code, this caused JPA exception, a combination that also doesn't make sense I assume (that was much easier to find since it also happened in DEV mode, but it would also be better to get a warning or an error in that case that explains that the options do not fit together).