glsl: Added gl_shader_state::EmitContReturn field

This is the start of a glsl-continue-return feature branch to support
a GLSL code generator option for 'continue' and 'return' statements.
Some targets don't support CONT or RET statements so we'll need to
try to generate code that does not use them...
diff --git a/src/mesa/shader/shader_api.c b/src/mesa/shader/shader_api.c
index 644cd39..cf9f8b9 100644
--- a/src/mesa/shader/shader_api.c
+++ b/src/mesa/shader/shader_api.c
@@ -402,6 +402,7 @@
     * are generated by the GLSL compiler.
     */
    ctx->Shader.EmitHighLevelInstructions = GL_TRUE;
+   ctx->Shader.EmitContReturn = GL_TRUE;
    ctx->Shader.EmitCondCodes = GL_FALSE;
    ctx->Shader.EmitComments = GL_FALSE;
    ctx->Shader.Flags = get_shader_flags();