glsl: Clarify error message about whole-array assignment in GLSL 1.10.

glsl: Clarify error message about whole-array assignment in GLSL 1.10.

Previously, it would produce:

    Failed to compile FS: 0:6(7): error: non-lvalue in assignment

and now it produces:

    Failed to compile FS: 0:5(7): error: whole array assignment is not
    allowed in GLSL 1.10 or GLSL ES 1.00.

Also, add spec quotation to the two places we have code for array
lvalues in GLSL 1.10.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>