[Piglit] UBO piglit test

[Vincent Lejeune]

Hi,

Here come several tests that checks UBO support.
The std140 layout is almost the same as the one in december.

The second one adds some syntax to shader_test files (it was partially rewritten) :
- "ubo-create [uboname]" generates a buffer whose size is the one reported by UBO API for uboname,
this ubo is later identified by its position in order of appearance, starting from 0.
- "ubo-uniform [bufferid] [type] [name] [content]" writes [contents] inside [bufferid], where [name] variable of type [type]  is stored.
(the type must be provided in order to fill whole structure of [name]).
- "ubo-bind [bufferid]" binds [bufferid] with its corresponding UBO in program.

The third one modify variable-read-script.sh so that it generates UBO tests that are ports of uniform reading test.

Regards,
Vincent