ui: yield unchanged values in walkconfig
Ever since walkconfig was introduced back in 25e7ea0f2cff, the values
yielded has been mutated by replacing "\n" with "\\n". This makes
walkconfig less useful than it could and there is no other way to
iterate over all config sections.
The third-party reposettings extension used ui.walkconfig but did not
take the replacement into account -- this change will actually fix a
bug in the extension when a value contains a newline.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a