fix: add :enabled sub-config for fixer tools
This allows distributing opt-in fixer tool configurations in .hgrc
files. This may be useful for adding default configs in core, or for
orgranizations that want to provide configs to their users.
Tools are still enabled by default because it would be confusing to add a
config and find that it has no effect until you add enabled=true.
Differential Revision: https://phab.mercurial-scm.org/D6975
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..