glsl: Make condition_to_hir() callable from outside ast_iteration_statement.

In addition to making it public, we also need to change its first
argument from an ir_loop * to an exec_list *, so that it can be used
to insert the condition anywhere in the IR (rather than just in the
body of the loop).

This will be necessary in order to make continue statements work
properly in do-while loops.

Cc: mesa-stable@lists.freedesktop.org
glsl: Fix continue statements in do-while loops.

From the GLSL 4.40 spec, section 6.4 (Jumps):

    The continue jump is used only in loops. It skips the remainder of
    the body of the inner most loop of which it is inside. For while
    and do-while loops, this jump is to the next evaluation of the
    loop condition-expression from which the loop continues as
    previously defined.

Previously, we incorrectly treated a "continue" statement as jumping
to the top of a do-while loop.

This patch fixes the problem by replicating the loop condition when
converting the "continue" statement to IR.  (We already do a similar
thing in "for" loops, to ensure that "continue" causes the loop
expression to be executed).

Fixes piglit tests:
- glsl-fs-continue-inside-do-while.shader_test
- glsl-vs-continue-inside-do-while.shader_test

Cc: mesa-stable@lists.freedesktop.org
!UPSTREAM: Work around bug in AntTweakBar

AntTweakBar tries to use glGetString(GL_EXTENSIONS) when connected to
a core context (it should use glGetStringi()).  Go ahead and allow
this for the time being.