and adjust the MULTISPACE one to use plural

In order to check the actual code better, checksrc now ignores
everything that look like preprocessor instructions. It also means
that code in macros are now longer checked.

Note that some rules then still don't need to be followed when code is
exactly below a cpp instruction.

Removes two checksrc exceptions we needed previously because of
preprocessor lines being checked.

Reported-by: Marcel Raad
Fixes #7863
Closes #7864

... to let curl_easy_escape() itself do the strlen. This avoids a (false
positive) Coverity warning and it avoids us having to store the strlen()
return value in an int variable.

Reviewed-by: Daniel Gustafsson
Closes #7862

... and update the includes to match how current htmltidy wants them
used.

Reported-by: Stathis Kapnidis
Fixes #7860
Closes #7861

- Make content length (ie download size) accessible to the user in the
  header callback, but only after all headers have been processed (ie
  only in the final call to the header callback).

Background:

For a long time the content length could be retrieved in the header
callback via CURLINFO_CONTENT_LENGTH_DOWNLOAD_T as soon as it was parsed
by curl.

Changes were made in 8a16e54 (precedes 7.79.0) to ignore content length
if any transfer encoding is used. A side effect of that was that
content length was not set by libcurl until after the header callback
was called the final time, because until all headers are processed it
cannot be determined if content length is valid.

This change keeps the same intention --all headers must be processed--
but now the content length is available before the final call to the
header function that indicates all headers have been processed (ie
a blank header).

Bug: https://github.com/curl/curl/commit/8a16e54#r57374914
Reported-by: sergio-nsk@users.noreply.github.com

Co-authored-by: Daniel Stenberg

Fixes https://github.com/curl/curl/issues/7804
Closes https://github.com/curl/curl/pull/7803

User sets the post fields size for binary data.  Hence, we should not be
using strlen on it.

Added test 1937 and 1938 to verify.

Closes #7844

Closes #7859