mesa: glsl: fix a number of glUniform issues

mesa: glsl: fix a number of glUniform issues

Additional error checking.
Allow setting elements of uniform arrays.  This involves encoding both
a uniform location and a parameter offset in the value returned by
glGetUniformLocation().
Limit glUniform[if]v()'s count to the size of the uniform array.
When setting bool-valued uniforms, convert all float/int values to 0 or 1.