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.
#!/bin/sh
hg init a
cd a
touch empty1
hg add empty1
hg commit -m 'add empty1' -d '1000000 0'
touch empty2
hg add empty2
hg commit -m 'add empty2' -d '1000000 0'
hg up -C 0
touch empty3
hg add empty3
hg commit -m 'add empty3' -d '1000000 0'
hg heads
hg merge 1
# before changeset 05257fd28591, we didn't notice the
# empty file that came from rev 1.
hg status
hg commit -m merge -d '1000000 0'
hg manifest --debug tip