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 test
cd test
mkdir da
echo foo > da/foo
echo foo > foo
hg ci -Ambase -d '0 0'
hg serve -p 20060 -d --pid-file=hg.pid
echo % manifest
("$TESTDIR/get-with-headers.py" localhost:20060 '/file/tip/?style=raw')
("$TESTDIR/get-with-headers.py" localhost:20060 '/file/tip/da?style=raw')
kill `cat hg.pid`