Don't try to determine interactivity if ui() called with interactive=False. WSGI applications are not supposed to refer to sys.stdin. In ed6df6b1c29a, hgweb and hgwebdir were fixed to pass interactive=False to their ui()'s, but sys.stdin.isatty() was still called by the ui objects. This change makes sure only the ui.fixconfig() method will call ui.isatty() (by making the ui._readline() method, which is currently only called from ui.prompt(), private). ui.fixconfig() is changed to let config files override the initial interactivity setting, but not check isatty() if interactive=False was specified in the creation of the ui.

% create source repository
adding a
% fork source repository
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b
% update source repository
% merge repositories
pulling from ../t2
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
% rename b as c
A c
R b
% rename back c as b