Reported-by: Bruce Stephens

Fixes #1098

Follow-up to 502acba2

Coverity CID 1374359 pointed out the unused result value.

Coverity CID 1374358

.. because including those headers helps Visual Studio's Intellisense.

..because they're no longer needed in the tool build. strcase is still
built by the libcurl project and exports curl_str(n)equal which is used
by the curl tool.

Bug: https://github.com/curl/curl/commit/9363f1a#all_commit_comments

... and now it avoids using the libcurl toupper() function

follow-up to 46133aa5

...to use the public function curl_strnequal(). This isn't ideal because
it adds extra overhead to any internal calls to checkprefix.

follow-up to 95bd2b3e

Suggested-by: Dan Jacobson
Issue: https://github.com/curl/curl/issues/1097

... since the curlx_* code no longer provides one and we don't link
libcurl to these test servers.

As they are after all part of the public API. Saves space and reduces
complexity. Remove the strcase defines from the curlx_ family.

Suggested-by: Dan Fandrich
Idea: https://curl.haxx.se/mail/lib-2016-10/0136.html

follow-up to 811a693b

This should fix the "warning: 'curl_strequal' redeclared without
dllimport attribute: previous dllimport ignored" message and subsequent
link error on Windows because of the missing CURL_EXTERN on the
prototype.

Follow-up to 811a693b

This is a followup to commit 811a693b

Fix compile break from 811a693b

The internal version strcasecompare isn't available outside libcurl

follow-up to 4f8d0b6f. Since the darwinssl code breaks
otherwise. If you build without darwinssl 10.5 works fine.

as that is still part of the API, fix from 8fe4bd08

Fix bug from 811a693b

Mistake brought by 9c91ec77

These two public functions have been mentioned as deprecated since a
very long time but since they are still part of the API and ABI we need
to keep them around.

some more follow-ups to 811a693b

follow-up to 811a693b

... that will ignore lines that are too long to fit in the buffer.

CVE-2016-8615

Bug: https://curl.haxx.se/docs/adv_20161102A.html
Reported-by: Cure53

We had some confusions on when each function was used. We should not act
differently on different locales anyway.

... to make it less likely that we forget that the function actually
does case insentive compares. Also replaced several invokes of the
function with a plain strcmp when case sensitivity is not an issue (like
comparing with "-").

... otherwise example.com/PATH and example.com/path would be assumed to
be the same and they usually aren't!

CVE-2016-8616

Bug: https://curl.haxx.se/docs/adv_20161102B.html
Reported-by: Cure53

CVE-2016-8617

Bug: https://curl.haxx.se/docs/adv_20161102C.html
Reported-by: Cure53

If the requested size is zero, bail out with error instead of doing a
realloc() that would cause a double-free: realloc(0) acts as a free()
and then there's a second free in the cleanup path.

CVE-2016-8619

Bug: https://curl.haxx.se/docs/adv_20161102E.html
Reported-by: Cure53