This fixes a possible unitialized struct variable.

Attributes GH PR #867: https://github.com/ArcticaProject/nx-libs/pull/867

plus some minor formatting fixes

This check has already been done before we reach here.

Also add some comments about a condition that will never occur...

Attributes GH PR #857: https://github.com/ArcticaProject/nx-libs/pull/857

This makes them much more readable

This should disable clipboard but effictively did activate clipboard=both.

Right at the beginnigng of nxagentParseSingleOption we check for
"clipboard" and prepare argv and argc accordingly for
ddxProcessArgument. The removed code thus could never be reached.

"clipboard=something" does not need to be passed on, so return after
setting nxagentOptions accordingly. This fixes

[nx-X11/programs/Xserver/hw/nxagent/Args.c:1584]: (error) Uninitialized variable: argc

Attributes GH PR #868: https://github.com/ArcticaProject/nx-libs/pull/868

instead of a full copy. We still have our own function because we
need to handle the nxagentGlxTrap. This trap is now set before the
start of the dispatcher while it has been set only directly before
calling the dispatched function.

Saves ~50 duplicated lines.

Attributes GH PR #866: https://github.com/ArcticaProject/nx-libs/pull/866

DeleteWindow() is calling FreeWindowResources() which is calling
DisposeWindowOptional() which sets pWin->optional to NULL. So the now
removed code was never called. After removal DeleteWindow() is
identical to the dix version, so we use that one.

many functions are almost identical to dix. Mark the minimal changes.

The only difference to the dix version was a fprintf if compiled with
-D TEST.

Attributes GH PR #865: https://github.com/ArcticaProject/nx-libs/pull/865

no function change

Attributes GH PR #864: https://github.com/ArcticaProject/nx-libs/pull/864

NXxvdisp.c only exists to set/unset nxagentXvTrap before/after
dispatch. There's no need to duplicate the original code. We now
rename the original dispatch functions and call them in our dispatch
code.

Also drop check for sun and cygwin, as they never appeared in xorg
upstream code.

Attributes GH PR #863: https://github.com/ArcticaProject/nx-libs/pull/863

by calling the upstream function from dix/dispatch.c

remove ~80 duplicate lines

by calling upstream version from dispatch.c

Attributes GH PR #861: https://github.com/ArcticaProject/nx-libs/pull/861

instead of including it and creating NXextension.o we can simply use
the dix version. There are no NX specials anymore.

Attributes GH PR #859: https://github.com/ArcticaProject/nx-libs/pull/859