Previously, the `alias.term` and `alias.type` would fail if the source argument was hash-only, and there was no way to create an alias for a definition that didn't already have a name.  Also, the `replace.term` and `replace.type` *only* worked on hashes, and they had to be *full* hashes.

With this PR, the source of an alias can be a short hash (even of a definition that doesn't currently have a name in the namespace) along with a name or hash-qualified name from the current namespace as usual.

Let's make some hash-only aliases, now that we can. :mad-with-power-emoji:

``` ucm
scratch/main> alias.type ##Nat Cat

  Done.

scratch/main> alias.term ##Nat.+ please_fix_763.+

  Done.

```