mesa: make the number of draw buffers part of the texenv program key state

All the state that effects the program should be in the key.
This didn't help with bug 28169 but is a good fix anyway.

NOTE: this is a low-priority candidate for the 7.8 branch.  In practice,
this issue might never be hit.

src/mesa/main/state.c

@@ -565,7 +565,7 @@ _mesa_update_state_locked( GLcontext *ctx )
 
    /* Determine which state flags effect vertex/fragment program state */
    if (ctx->FragmentProgram._MaintainTexEnvProgram) {
-      prog_flags |= (_NEW_TEXTURE | _NEW_FOG |
+      prog_flags |= (_NEW_BUFFERS | _NEW_TEXTURE | _NEW_FOG |
 		     _NEW_ARRAY | _NEW_LIGHT | _NEW_POINT | _NEW_RENDERMODE |
 		     _NEW_PROGRAM);
    }

src/mesa/main/texenvprogram.c

@@ -98,6 +98,7 @@ struct state_key {
    GLuint fog_enabled:1;
    GLuint fog_mode:2;          /**< FOG_x */
    GLuint inputs_available:12;
+   GLuint num_draw_buffers:4;
 
    /* NOTE: This array of structs must be last! (see "keySize" below) */
    struct {
@@ -485,6 +486,9 @@ static GLuint make_state_key( GLcontext *ctx,  struct state_key *key )
       inputs_referenced |= FRAG_BIT_FOGC; /* maybe */
    }
 
+   /* _NEW_BUFFERS */
+   key->num_draw_buffers = ctx->DrawBuffer->_NumColorDrawBuffers;
+
    key->inputs_available = (inputs_available & inputs_referenced);
 
    /* compute size of state key, ignoring unused texture units */
@@ -1438,10 +1442,10 @@ create_new_program(GLcontext *ctx, struct state_key *key,
    p.program->Base.Parameters = _mesa_new_parameter_list();
    p.program->Base.InputsRead = 0x0;
 
-   if (ctx->DrawBuffer->_NumColorDrawBuffers == 1)
+   if (key->num_draw_buffers == 1)
       p.program->Base.OutputsWritten = 1 << FRAG_RESULT_COLOR;
    else {
-      for (i = 0; i < ctx->DrawBuffer->_NumColorDrawBuffers; i++)
+      for (i = 0; i < key->num_draw_buffers; i++)
 	 p.program->Base.OutputsWritten |= (1 << (FRAG_RESULT_DATA0 + i));
    }
 
@@ -1493,8 +1497,8 @@ create_new_program(GLcontext *ctx, struct state_key *key,
 
    cf = get_source( &p, SRC_PREVIOUS, 0 );
 
-   for (i = 0; i < ctx->DrawBuffer->_NumColorDrawBuffers; i++) {
-      if (ctx->DrawBuffer->_NumColorDrawBuffers == 1)
+   for (i = 0; i < key->num_draw_buffers; i++) {
+      if (key->num_draw_buffers == 1)
 	 out = make_ureg( PROGRAM_OUTPUT, FRAG_RESULT_COLOR );
       else {
 	 out = make_ureg( PROGRAM_OUTPUT, FRAG_RESULT_DATA0 + i );