best effort to keep text/plain

[tkikuchi]

When a message come in different charset than list
specific one, Decorate.py adds the header and footer in
mime attatchments. This patch tries to keep the
good-old plain text format by making these texts into
unicode and encode in list preferred charset. If it
fails, the messages will get mime-multiparted as was
the case without this patch.

[tkikuchi (tkikuchi-users)]

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Expand this patch to base64 encoded plain text.
apply the second patch Decorate.py.diff2 to the original
Decorate.py

[tkikuchi (tkikuchi-users)]

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Refine the code and increment priority.

[tkikuchi (tkikuchi-users)]

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Sorry, there was a error in the previous patch.

[tkikuchi (tkikuchi-users)]

The file Decorate.py.patch.txt was added: Decorate.py.patch

[tkikuchi (tkikuchi-users)]

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If you personalize delivery, i18n user name cause error
because the name is stored in unicode. I merge this fix into
this Decorate.py.patch.txt

[tkikuchi (tkikuchi-users)]

The file Decorate.py.patch.txt was added: Decorate.py.patch (with personalization fix)

[tkikuchi (tkikuchi-users)]

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merged into #865661.