Avoid an ambiguous occurence for 'findFile'

Fix for clashing definition of 'findFile' with the one exported from System.Directory. This is the error message on my system -

```
Resolving dependencies...
Configuring grm-0.1.1...
Building grm-0.1.1...
Preprocessing library grm-0.1.1...
[1 of 3] Compiling Grm.Prims        ( Grm/Prims.hs, dist/build/Grm/Prims.o )

Grm/Prims.hs:199:35:
    Ambiguous occurrence `findFile'
    It could refer to either `Grm.Prims.findFile',
                             defined at Grm/Prims.hs:195:1
                          or `System.Directory.findFile',
                             imported from `System.Directory' at Grm/Prims.hs:19:1-23
cabal: Error: some packages failed to install:
grm-0.1.1 failed during the building phase. The exception was:
ExitFailure 1
```