Attributes GH PR #875: https://github.com/ArcticaProject/nx-libs/pull/875

fix one FIXME. This is a rewritten and extended version of a quick
patch by Danil Pleshakov and Dimbor.

Correctly determine the Atom names from the real X server.

The previously used "Atom" type was confusing. Clarify this by
writing the code as requested in the manpage of XChangeProperty:

"If the specified format is 8, the property data must be a char array.
If the specified format is 16, the property data must be a short
array.  If the specified format is 32, the property data must be a
long array."

Attributes GH PR #860: https://github.com/ArcticaProject/nx-libs/pull/860

make i a local loop variable everywhere by changing the while loop to
a for loop.

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.