Only read .hg/hgrc files from trusted users/groups
The list of trusted users and groups is specified in the [trusted]
section of a hgrc; the current user is always trusted; "*" can be
used to trust all users/groups.
Global hgrc files are always read.
On Windows (and other systems that don't have the pwd and grp modules),
all .hg/hgrc files are read.
This is essentially the same patch that was previously applied as
revision 494521a3f142.
port:4:export
port:4:vaportight
port:4:import/export
port:4:4:-:spam:import/export
port:3:4:+:eggs:import/export
port:2:1:-:spam:import
port:2:2:-:spam:export
port:2:1:+:spam:export
port:2:2:+:spam:vaportight
port:2:3:+:spam:import/export
port:1:2:+:eggs:export
port:0:1:+:eggs:import
port:4:import/export
% follow
port:0:import
port2:6:4:+:eggs:deport
port:4:4:-:spam:import/export
port:3:4:+:eggs:import/export
port:2:1:-:spam:import
port:2:2:-:spam:export
port:2:1:+:spam:export
port:2:2:+:spam:vaportight
port:2:3:+:spam:import/export
port:1:2:+:eggs:export
port:0:1:+:eggs:import