i965/gen7: Emit workaround flush when changing GS enable state.
glsl: Rework interface block linking.

Previously, when doing intrastage and interstage interface block
linking, we only checked the interface type; this prevented us from
catching some link errors.

We now check the following additional constraints:

- For intrastage linking, the presence/absence of interface names must
  match.

- For shader ins/outs, the interface names themselves must match when
  doing intrastage linking (note: it's not clear from the spec whether
  this is necessary, but Mesa's implementation currently relies on
  it).

- Array vs. nonarray must be consistent, taking into account the
  special rules for vertex-geometry linkage.

- Array sizes must be consistent (exception: during intrastage
  linking, an unsized array matches a sized array).

Note: validate_interstage_interface_blocks currently handles both
uniforms and in/out variables.  As a result, if all three shader types
are present (VS, GS, and FS), and a uniform interface block is
mentioned in the VS and FS but not the GS, it won't be validated.  I
plan to address this in later patches.

Fixes the following piglit tests in spec/glsl-1.50/linker:
- interface-blocks-vs-fs-array-size-mismatch
- interface-vs-array-to-fs-unnamed
- interface-vs-unnamed-to-fs-array
- intrastage-interface-unnamed-array