#12 crashes on unexpected files in datastore

[Hallvord R. M. Steen]

I often see Rapple crashing because the datastore directories contain files that aren't in the current source directory.

Can usually be reproduced by doing a build, removing a file from source folder and trying another build.

I'd like Rapple to empty the datastore automatically after a build (with a command line switch to *disable* this behaviour for debugging).