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.

% should display baz only
? baz
--
A dir/b.o
? a.c
? a.o
? dir/c.o
? syntax
--
abort: .hgignore: invalid pattern (relre): *.o
--
A dir/b.o
? .hgignore
? a.c
? syntax
--
A dir/b.o
? .hgignore
? a.c
? syntax
--
A dir/b.o
? .hgignore
? a.c
? syntax
--
A dir/b.o
? .hgignore
? a.c
? syntax
--
.hgignore: ignoring invalid syntax 'invalid'
A dir/b.o
? .hgignore
? a.c
? a.o
? dir/c.o
? syntax
--
A dir/b.o
? .hgignore
? a.c
? syntax
--
A dir/b.o
? .hgignore
? a.c
? a.o
? dir/c.o
--
A dir/b.o
--
A b.o