hooks: add a `auto` value for `hooks.*run-with-plain`...
hooks: add a `auto` value for `hooks.*run-with-plain`
That setting restore the behavior pre-5.6. The current HGPLAIN value is simply
passed to the hooks.
This allow user who needs it to fully mitigate the behavior change introduced
in Mercurial 5.7 by restoring the older behavior.
Differential Revision:
https://phab.mercurial-scm.org/D9982
