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.
adding foo
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% should fail
pulling from ../tt
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
not updating, since new heads added
(run 'hg heads' to see heads, 'hg merge' to merge)
% should fail
pulling from ../t
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
not updating, since new heads added
(run 'hg heads' to see heads, 'hg merge' to merge)
merging foo
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
% should work
pulling from ../tt
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (-1 heads)
1 files updated, 0 files merged, 0 files removed, 0 files unresolved