config: use the new '_unset' value for 'configbool'
This should let 'configbool' delegate all special processing of the default
config value to the main 'config' method.
The default value for bool (False) is still enforced in this method if no other
default were passed.
$ hg init a
$ cd a
$ hg init b
$ echo x > b/x
Should print nothing:
$ hg add b
$ hg st
$ echo y > b/y
$ hg st
Should fail:
$ hg st b/x
abort: path 'b/x' is inside nested repo 'b' (glob)
[255]
$ hg add b/x
abort: path 'b/x' is inside nested repo 'b' (glob)
[255]
Should fail:
$ hg add b b/x
abort: path 'b/x' is inside nested repo 'b' (glob)
[255]
$ hg st
Should arguably print nothing:
$ hg st b
$ echo a > a
$ hg ci -Ama a
Should fail:
$ hg mv a b
abort: path 'b/a' is inside nested repo 'b' (glob)
[255]
$ hg st
$ cd ..