save settings from untrusted config files in a separate configparser
This untrusted configparser is a superset of the trusted configparser,
so that interpolation still works.
Also add an "untrusted" argument to ui.config* to allow querying
ui.ucdata.
With --debug, we print a warning when we read an untrusted config
file, and when we try to access a trusted setting that has one value
in the trusted configparser and another in the untrusted configparser.
adding base
foo/renamed
renamed
bar/renamed
renamed
baz
.hg/patches/baz