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.

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pulling from ../a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
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merging testdir/subdir/a and testdir/a
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(branch merge, don't forget to commit)
M testdir/subdir/a
diff -r d02b3fc32762 testdir/subdir/a
--- a/testdir/subdir/a
+++ b/testdir/subdir/a
@@ -1,1 +1,1 @@ a
-a
+alpha