Re: i18n.logToUTF8: convert commit log message to UTF-8

Hi,

I don't like the convention to add the encoding after a trailing NUL. I'd 
rather have it as an "encoding blabl" header like the author and committer 
headers. I.e.

-- snip --
tree 519fba5ec35f25cbac7f46574f214fb5eb95d2c8
parent 41c7c86ccbcb846cacf48c5e283983fa797cf37b
author Johannes Schindelin [off-list ref] 1166969650 +0100
committer Johannes Schindelin [off-list ref] 1166969650 +0100
encoding latin1

    git-commit-tree: add encoding header if commitEncoding != utf-8
-- snap --

Our log routines all grok these commit objects.

And I would prefer commit-tree to fail if we explicitely ask for 
conversion to UTF-8, but NO_ICONV is set, or reencoding fails for other 
reasons.

Ciao,
Dscho