The quote_rfc2047() always adds RFC2047 quoting. To avoid
quoting ASCII subjects, before calling quote_rfc2047()
subject must be tested for non-ASCII characters. This patch
introduces a new quote_subject() function, which performs
the test and calls quote_rfc2047 only if necessary.
Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net> Signed-off-by: Jeff King <peff@peff.net>