gettext: setlocale(LC_CTYPE, "") breaks Git's C function assumptions

gettext: setlocale(LC_CTYPE, "") breaks Git's C function assumptions

Remove the setlocale/LC_CTYPE call from gettext.c, we only need
setlocale/LC_MESSAGES to use the message catalog, and setting LC_CTYPE
from the environment breaks Git's assumptions about C library
functions.

Under a non-C locale functions like vsnprintf become locale sensitive,
so that they'll e.g. refuse to process ISO-8895-1 data under a UTF-8
locale.

This triggered a "your vsnprintf is broken" error on Git's own
repository when inspecting v0.99.6~1 under a UTF-8 locale.

That commit contains a ISO-8859-1 encoded author name, which the
locale aware vsnprintf(3) won't interpolate in the format argument,
due to mismatch between the data encoding and the locale.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>