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
# test command parsing and dispatch
hg init a
cd a
echo a > a
hg ci -Ama -d '0 0'
echo "# missing arg"
hg cat
echo '% [defaults]'
hg cat a
cat > $HGRCPATH <<EOF
[defaults]
cat = -v
EOF
hg cat a
echo '% no repo'
cd ..
hg cat
exit 0