[Xcb] XCBImage tests

[Vincent Torri]

Hello,

in xcb-demo, i've added 2 tests for XCBImage:

1) julia: Use of XCBImage with a colormap

2) lissajoux: animation of a lissajoux curve, with support of shm (if
availaible), with a small bench at the end of the 20s length animation.

well, right now, the shm support is broken, and even sometimes, the
standard one crashes. And i don't know why.

If someone, one day, wants to find out where are the bugs, i would be
pleased to know :)

Another question : what filename should i use for the convenient functions
that i want to write ? xcb-macros.c ? xcb-convenient.c ?

regards

Vincent