obsolete: introduce an `_enabled` switch to disable the feature by default
Obsolete markers wide-usage and propagation should be avoided by default until
the obsolete feature is more mature.
This changeset introduce the `_enable` variable and prevent the creation of
obsolete marker if the feature is set to `False` (the default).
More limitation comes in followup changesets.
$ cat > unix2mac.py <<EOF
> import sys
>
> for path in sys.argv[1:]:
> data = file(path, 'rb').read()
> data = data.replace('\n', '\r')
> file(path, 'wb').write(data)
> EOF
$ cat > print.py <<EOF
> import sys
> print(sys.stdin.read().replace('\n', '<LF>').replace('\r', '<CR>').replace('\0', '<NUL>'))
> EOF
$ hg init
$ echo '[hooks]' >> .hg/hgrc
$ echo 'pretxncommit.cr = python:hgext.win32text.forbidcr' >> .hg/hgrc
$ echo 'pretxnchangegroup.cr = python:hgext.win32text.forbidcr' >> .hg/hgrc
$ cat .hg/hgrc
[hooks]
pretxncommit.cr = python:hgext.win32text.forbidcr
pretxnchangegroup.cr = python:hgext.win32text.forbidcr
$ echo hello > f
$ hg add f
$ hg ci -m 1
$ python unix2mac.py f
$ hg ci -m 2
attempt to commit or push text file(s) using CR line endings
in dea860dc51ec: f
transaction abort!
rollback completed
abort: pretxncommit.cr hook failed
[255]
$ hg cat f | python print.py
hello<LF>
$ cat f | python print.py
hello<CR>