o Install nxagent/nxproxy executables into multi-arch path.
  o Fake libNX_X11.so* as $LIBDIR/nx-X11/libX11.so*.
  o Allow injecting different $NXAPP containing the executable name.

  o For e.g. x2goagent this requires the following changes:

    - Move x2goagent symlink from /usr/lib/x2go/bin/x2goagent to
      $LIBDIR/nx/bin/x2goagent
    - Replace /usr/bin/x2goagent by a two-liner...

    ```
    #!/bin/sh

    export NXAPP=x2goagent
    nxagent
    ```