Jeff King authored May 22, 2014 and Junio C Hamano committed May 27, 2014

Since the previous commit, we now give a sanitized,
shortened version of the content-type header to any callers
who ask for it.

This patch adds back a way for them to cleanly access
specific parameters to the type. We could easily extract all
parameters and make them available via a string_list, but:

  1. That complicates the interface and memory management.

  2. In practice, no planned callers care about anything
     except the charset.

This patch therefore goes with the simplest thing, and we
can expand or change the interface later if it becomes
necessary.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>