Previously it rendered the page from files matching "*.d" in the correct
directory, which worked fine in git builds when the files were added but
made it easy to forget adding the files to the dist.

Now, only man page sections listed in DPAGES in Makefile.inc will be
used, thus "forcing" us to update this to get the man page right and get
it included in the dist at the same time.

Ref: #5146
Closes #5149

... to also make it update when we remove files, like we did for
--environment in commit a8e388dd1095.

For easier sharing with CMake. The contents were reformatted to use
two-space indent and expanded tabs (matching lib/Makefile.common).

Ref: https://github.com/curl/curl/pull/1288

- Add new option CURLOPT_SUPPRESS_CONNECT_HEADERS to allow suppressing
  proxy CONNECT response headers from the user callback functions
  CURLOPT_HEADERFUNCTION and CURLOPT_WRITEFUNCTION.

- Add new tool option --suppress-connect-headers to expose
  CURLOPT_SUPPRESS_CONNECT_HEADERS and allow suppressing proxy CONNECT
  response headers from --dump-header and --include.

Assisted-by: Jay Satiro
Assisted-by: CarloCannas@users.noreply.github.com
Closes https://github.com/curl/curl/pull/783

In addition to unix domain sockets, Linux also supports an
abstract namespace which is independent of the filesystem.

In order to support it, add new CURLOPT_ABSTRACT_UNIX_SOCKET
option which uses the same storage as CURLOPT_UNIX_SOCKET_PATH
internally, along with a flag to specify abstract socket.

On non-supporting platforms, the abstract address will be
interpreted as an empty string and fail gracefully.

Also add new --abstract-unix-socket tool parameter.

Signed-off-by: Isaac Boukris <iboukris@gmail.com>
Reported-by: Chungtsun Li (typeless)
Reviewed-by: Daniel Stenberg
Reviewed-by: Peter Wu
Closes #1197
Fixes #1061