Without this change I get CMake errors due to use of ${FLTK_INCLUDE_DIR}
and references to the non-existent vncviewer target.

Xvnc was originally based on Xvfb, but it's just confusing to keep the
names. So change all prefix to "vnc" instead to clearly mark things as
part of TigerVNC.

It isn't really useful as it behaves just like starting multiple
servers, so remove it in favour of keeping things simple.

This is a development flag with no real use, so remove it to clean up
the code.

Remove stuff we don't use, and get it more in sync with Xvfb for easier
comparison.

This was removed years ago.

The memory leak this worked around was fixed in X.org 1.16.

Keep everything in one place to make it easier to read.

This also removes the call to RRInit() as that is done implicitly
anyway.

There's been a common one since X.org 1.11, so use that instead of our
own copy.

We don't build for that platform anyway, so this is just a remnant from
Xvfb.

With the 1.20.x releases there has been features and API changes even on
patch level versions, so we need to update our macros to handle these as
well.

This is a pointless remnant of Xvfb. We never print the id of the shared
memory, so no other application can access this memory anyway.

This hasn't been supported or used in many years, so clean out the final
remnants.

This hasn't been used since xorg-server 1.1 so get rid of it.

This is consistent with other ddx behaviour.

This is what all the other ddx variants use, so do the same in Xvnc to
be consistent.

Makes it easier to compare with upstream files as the formatting will be
the same.

RENDER has been mandatory since xorg-server 1.9, so remove these
checks.

This should only be in the ddx parts of an X server, and Input.c is used
by libvnc.so as well and can cause conflicts there.

This was removed from Ubunut's X.org packages years ago, so drop it from
our packing as well.

We miscalculated the screen layout if the geometry had an offset as we
adjusted the real screen layout to account for the offset, but compared
it to the unadjusted geometry.

Is a lot more useful default than the previous "x11", or "x0vncserver".
At the same time give x0vncserver a parameter to change the name.

Let's avoid making this too complex and force every user to know about
magical functions.

Allows the default value to be dynamically generated in a buffer that is
reused.

Better to just hide these parameters rather than stating that they are
unused in the man page.

Our current architecture doesn't support waiting for a response here, so
don't even try or we'll just get an error.

The session might have died, or failed to initialise properly, so be
prepared for gnutls_bye() to be unable to do its job.

We would leak the security module below the top client VeNCrypt module,
meaning that those modules would not get a chance to shut down
gracefully.

It's perfectly safe to delete NULL pointers, so simplify things by
removing these checks.

Gives us a more meaningful error rather than just "Error in push/pull
function".

Having this early check means that we somewhat randomly get different
exception behaviours on errors in deeper layers as some exceptions are
allowed to propagate unhindered and some are not (since they are thrown
in the pull function).

Give GnuTLS the correct errno from deeper layers, in the cases where we
know it. In most cases GnuTLS doesn't care, but just in case...

Travis has unfortunately been severely rate limited by Docker Hub so we
have to switch to GitHub, which has an agreement with Docker to avoid
the rate limiting.

No TTY is provided in GitHub's environment, so we cannot have this flag.

Otherwise cmake breaks as it requires a newer version without properly
listing that in its dependencies.

These are incompatible with functions such as gettext() as clang hasn't
implemented the function attribute function_arg.

A initial workflow needs to be defined for actions to trigger on pull
requests, so just add a minimal, dummy one.