extract_content_type() could not extract a charset parameter if the
parameter is not the first one and there is a whitespace and a following
semicolon just before the parameter. For example:

    text/plain; format=fixed ;charset=utf-8

And it also could not handle correctly some other cases, such as:

    text/plain; charset=utf-8; format=fixed
    text/plain; some-param="a long value with ;semicolons;"; charset=utf-8

Thanks-to: Jeff King <peff@peff.net>
Signed-off-by: NYi EungJun <eungjun.yi@navercorp.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

We currently recognize an error message with a content-type
"text/plain; charset=utf-16" as text, but we ignore the
charset parameter entirely. Let's encode it to
log_output_encoding, which is presumably something the
user's terminal can handle.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When we get a content-type from curl, we get the whole
header line, including any parameters, and without any
normalization (like downcasing or whitespace) applied.
If we later try to match it with strcmp() or even
strcasecmp(), we may get false negatives.

This could cause two visible behaviors:

  1. We might fail to recognize a smart-http server by its
     content-type.

  2. We might fail to relay text/plain error messages to
     users (especially if they contain a charset parameter).

This patch teaches the http code to extract and normalize
just the type/subtype portion of the string. This is
technically passing out less information to the callers, who
can no longer see the parameters. But none of the current
callers cares, and a future patch will add back an
easier-to-use method for accessing those parameters.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since commit 426e70d4 (remote-curl: show server content on
http errors, 2013-04-05), we relay any text/plain error
messages from the remote server to the user. However, we
never tested it.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>