This patch adds the ability for shader_runner tests to include a
"[vertex data]" section containing data in columnar format, for example:

[vertex data]
vertex/float/3 foo/uint/1 bar/int/2
0.0 0.0 0.0    0xe0000000 0 0
0.0 1.0 0.0    0x70000000 1 1
1.0 1.0 0.0    0x00000000 0 1

Each column header is of the form ATTRNAME/TYPE/COUNT, where ATTRNAME
is the name of the vertex attribute to be bound to this column, TYPE
is the type of data that follows ("float", "int", or "uint"), and
COUNT is the vector length of the data (e.g. "3" for vec3 data).

To send vertex data to the shader, use the new shader_runner command
"draw arrays".  The parameters are the same as for the glDrawArrays()
command, so for example to draw triangle primitives using 3 elements
from the vertex data array starting at element 0, use the command:

draw arrays GL_TRIANGLES 0 3

More detailed examples can be found in the tests/shaders/vbo
directory.

The implementation is largely in a new file, piglit-vbo.cpp, so that
it can be re-used by other piglit tests if necessary.