Cache another layer of directories in PrecompilationStore::File
Cache another layer of directories in PrecompilationStore::File

Saves another couple 100 calls to .child and speeds up loading GTK::Simple from
2.5 to 2.1 seconds.
Caching the full .path however would lead to spectest regressions.

tbrowder/rakudo,Gnouc/rakudo,raydiak/rakudo,jonathanstowe/rakudo,salortiz/rakudo,awwaiid/rakudo,tbrowder/rakudo,rakudo/rakudo,tony-o/rakudo,MasterDuke17/rakudo,salortiz/rakudo,MasterDuke17/rakudo,salortiz/rakudo,labster/rakudo,Gnouc/rakudo,nbrown/rakudo,usev6/rakudo,awwaiid/rakudo,tony-o/rakudo,tbrowder/rakudo,softmoth/rakudo,Gnouc/rakudo,samcv/rakudo,salortiz/rakudo,samcv/rakudo,awwaiid/rakudo,lucasbuchala/rakudo,labster/rakudo,rakudo/rakudo,labster/rakudo,jonathanstowe/rakudo,rakudo/rakudo,lucasbuchala/rakudo,nbrown/rakudo,samcv/rakudo,jonathanstowe/rakudo,tony-o/rakudo,usev6/rakudo,raydiak/rakudo,sjn/rakudo,salortiz/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,salortiz/rakudo,samcv/rakudo,lucasbuchala/rakudo,rakudo/rakudo,nbrown/rakudo,samcv/rakudo,raydiak/rakudo,nbrown/rakudo,tony-o/rakudo,nbrown/rakudo,awwaiid/rakudo,lucasbuchala/rakudo,softmoth/rakudo,tbrowder/rakudo,raydiak/rakudo,usev6/rakudo,Gnouc/rakudo,lucasbuchala/rakudo,rakudo/rakudo,sjn/rakudo,MasterDuke17/rakudo,jonathanstowe/rakudo,labster/rakudo,softmoth/rakudo,softmoth/rakudo,usev6/rakudo,labster/rakudo,nbrown/rakudo,awwaiid/rakudo,usev6/rakudo,tony-o/rakudo,Gnouc/rakudo,softmoth/rakudo,sjn/rakudo,sjn/rakudo,jonathanstowe/rakudo,labster/rakudo,tony-o/rakudo,MasterDuke17/rakudo,rakudo/rakudo,sjn/rakudo,tbrowder/rakudo