Priority: medium

Add commands `reference-tree' and `reference-file' which 
find a pristine copy but don't tell you from where (maybe library,
maybe ++prisine cache, maybe some future location).

Use this in lots of places in the code search for pristine copies.

Add a space-bound cache, get rid of ++pristine trees.


# tag: Tom Lord Thu Jan 23 02:21:20 2003 (features/unified-caches)
#

