In messages printed by the evaluator, we use showType(.) to say things
like "expected X, got Y" where X, Y can be string, string with context,
etc.
After changes in the Lix data model (pointer tagging and friends), paths
got squished inside a internal string type.
We missed updating `showType` to take this fact into account which
caused an unfortunate:
`error: expected a string but found a string with context:
/nix/store/wjf8rdpp63rhyasbzc7zfms1agf7pwyd-source`
while using a path on `builtins.getContext`
A test is added.
Change-Id: Ifb0129ead2ea1973fc17dc0133f8a694995536b1
Signed-off-by: Raito Bezarius <raito@lix.systems>