Unflops the spur in +en-beam, +de-beam, and everything that calls either
of those, or works with the consequences of their output.
This includes clay's interface for mounting and unmounting, which now
no longer expects the arguments to contain an old-style spur.
Barebones 2-way diff thread. Further development should include:
- recognize at least %txt and %hoon diff types as (urge:clay cord) and
print them prettily
- check if they're directories and recurse through them, noting files
that exist in one or the other and diffing ones that exist in both
- support 3-way diffs. Since we know the desks they're on, we can find
a mergebase (see how +trouble gets the base-hash in #3378) and do a
3-way diff.
- extend the above to support all the useful diffs, including
diff3(a,b), diff2(mergebase(a,b),a) and any other useful ones.
