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Even though I think this patch is correct in principle, I
see a few problems with it:
1. Since it doesn't fix a bug, it probably cannot go into 2.2.
2. There is no autoconf test for mbtowc. You should test
this in configure, and then conditionalize your code on
HAVE_MBTOWC.
3. There is too much code duplication. Try to find a
solution which special-cases the escape codes (\something)
only once. For example, you may implement a trivial mbtowc
redefinition if mbtowc is not available, and then use mbtowc
always.