[Xcb] [XCB] OPW applicant's testcase for changing <valueparam> to <switch> in render extension

[Asalle Kim]

Good evenig,

I am an OPW Round 9 applicant. I am interested to become an intern of
XCB server-side project under the mentorship of Christian Linhart.

As my initial contribution I made a little testcase for Jaya's changes 
in render.xml
with some very valuable advices and help of Christian.

The testcase should view blank screen, after user presses any key a blue 
rect
should be painted, after another key pressing a cyan line should be painted.
After the last key pressing the window holds waiting for interrupt signal
(usually emited with Ctrl+C combination).

This testcase uses the xcb_render_create_picture_checked function and some
others. I tried to
     * run testcase connecting to prior to Jaya's changes version of the 
library, then to the
     improved version using the LD_LIBRARY_PATH (not re-compiling sources
     with the new version) both work the same way, this shows
     binary backward compatibility of the Jaya's changes.

     * compile testcase with the sources of the improved library and 
then run,
     it also works as expected and shows the source code compability of 
improved version.

     * run some programs(eog, shotwell) with the improved version -- it 
works as usual.

I believe this proves that Jaya's change are backward compatible.

This task was rather challenging for me and also a great experience; I 
am very thankful
to OPW and Christian Linhart personally for giving me an unique opportunity
to contribute a bit to such a great and widely used project.

Best regards,
Asalle