Linux implementation using ffmpeg

It's difficult to support both old and new versions, so raise the
requirement to the oldest that is commonly used, which is CMake 3.10.2
on Ubuntu 18.04.

Or rpmbuild gets grumpy.

Add missing build requirements: libpng-devel, zlib-devel

Remove obsolete build requirements: libXfont-devel

Fix unexpected rpm macro expansion `%{VERSION}` which is supposed
to be passed through as literal to `rpm -q --qf`. This hasn't
caused problems before, but it was found to cause problems when
built from EL 8 when it expanded to "1.10.1".

Update RPM package build process to automatically detect and apply
the correct X.org patch.

This makes our builds directly compatible with most distributions
without packagers/users having to specify extra flags.

Running as a service on a SELinux system requires rules so we can
transition to our own context. We also need the proper permissions
to start new user sessions.

This sets up a more correct session as there are key tasks that
need to be performed by PAM. E.g. systemd will allocate cgroups
and start base services.

In order to easily handle this as a system service the mapping of
displays is now done via a configuration file.

It is the most common init system these days so it should not be
hidden in the contrib/ directory.

This also removes all old SysV files from the contrib packages.

Install some example files to make things more easily discoverable.

Remove the unused Java self sign variable, and make sure we don't
hard code a version as it needs to be adjusted before a build.

It is needed by x0vncserver.

They include a new enough version, so stop doing our own build.

Applets don't work anymore so remove everything that has to do
with serving them.

See issue #534

OpenJDK 7u111 on el6 now throws an exception if the TSA URL scheme
is https.

These files are not Red Hat or Ubuntu specific, so install them
on all Unix systems where the viewer is installed.

Obsoleted by 7461517

Obsoleted by 7461517

Split the static library pre-reqs into a static-devel package
so that they don't need to be rebuilt everytime tigervnc's
sources change.

Several of the pre-requisites have outstanding CVEs.

The patch sources were removed but the %patch commands were
left in the spec files.

The patch sources were removed but the %patch commands were
left in the spec files.

This workaround is no longer needed as we've fixed the bad interaction
with libtool.

Make the dependency on g++ explicit.

Now that the native version of cmake in el6 has been bumped to
v2.8 we can remove the dependency on EPEL's cmake28 package.

Make the dependency on g++ explicit.

Now that the native version of cmake in el6 has been bumped to
v2.8 we can remove the dependency on EPEL's cmake28 package.

Requirement was an artifact of older version of mesa, and is no longer necessary.

Requirement was an artifact of older version of mesa, and is no longer necessary.

el5 and el6 need newer versions of gnutls (and it's prereqs) than are available natively.

el5 and el6 need newer versions of gnutls (and it's prereqs) than are available natively.

Xinerama was disabled in the redhat spec file that ours was adapted from.  Unsure why it was disabled in the first place.

Commit f0fffd4d7f makes ldnow patch unnecessary.
Commit 0dc36a501e makes format-security patch unnecessary.

Oops, didn't realize these changes wre on the branch from an
old pull request.

RHEL/CentOS 6.6 bumped the version of xorg to 6u6, which broke
software GLX because Xvnc wasn't properly linked against libglapi.

Some minor adjustments to sync up the el6 spec file with fedora.

RPM build failed when the self-signed cert was used because the macro did not
expand correctly.

* Removed the hard coded snap tag, if needed it should be passed in
  via "rpmbuild --define 'snap ...'".
* Changed the hard coded version to "@VERSION@" to make it clear
  that the copy of the spec file in the repository needs to be
  updated manually.