make mercurial look in more places for config files. now it searches <install dir>/etc/mercurial, /etc/mercurial, and user hgrc. this allows site-wide configuration to be shared over automounted nfs partition, instead of chenging on every system. option of having local configuration on every system remains. old code for searching /etc/mercurial/hgrc.d never worked, this code is tested and works.

%%% should show a removed and b added
A b
R a
reverting...
%%% should show b unknown and a back to normal
? b
merging a
%%% should show foo-b
foo-b
%%% should show a removed and b added
A b
R a
reverting...
%%% should show b unknown and a marked modified (merged)
? b
%%% should show foo-b
foo-b