context: switch ctx() use to changectx()...
context: switch ctx() use to changectx()
I added `ctx()` to `overlayworkingfilectx`, (and before that, `absentfilectx`),
because `absentfilectx` had reference to this function in its `cmp()` function.
But the standard is actually `changectx()`, and no other class implements
`ctx()`. So let's use the standard name.
(As a result, I'm not sure that part of the `absentfilectx` comparator ever
worked! It was written before I added either function.)
This will be necessary in the next patch.
Differential Revision:
https://phab.mercurial-scm.org/D1211
