Fix user/repo validator

I’m retarded
Cache by compilation unit, not "before" part of line

The "before" part of the line contains the method where the exception
passed through, which does not affect the file.

By ‘compilationUnit’, I mean the part
    com.redhat.ceylon.compiler.loader.AbstractModelLoader
of the line
    at com.redhat.ceylon.compiler.loader.AbstractModelLoader.cacheKeyByModule