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.
% initial svn import
Adding t/a
Committed revision 1.
% update svn repository
A t2/a
Checked out revision 1.
A b
Sending a
Adding b
Transmitting file data ..
Committed revision 2.
% convert to hg once
assuming destination trunk-hg
initializing destination trunk-hg repository
scanning source...
sorting...
converting...
1 init
0 changea
% update svn repository again
Sending a
Sending b
Transmitting file data ..
Committed revision 3.
% test incremental conversion
assuming destination trunk-hg
destination trunk-hg is a Mercurial repository
scanning source...
sorting...
converting...
0 changeb