Forcing encoding for "git commit"

["Constantine Plotnikov" <constantine.plotnikov@gmail.com>]

I would like to see a possibility to force encoding for the "git
commit" command. Currently only way to change encoding used by "git
commit" is to set "i18n.commitencoding" configuration variable. But
there is no way to override this variable for the specific commit like
it is possible for "show" and "log" commands.

This would be useful when git is invoked from the tools. Currently
tools have to query configuration variable and to encode message
according to the value of the variable. And it might happen that not
all characters produced by tool are supported by target encoding.
Forcing the encoding, would have allowed the tool use the suitable
encoding without changing user preferences.

Regards,
Constantine