mesa: support boolean and integer-based parameters in prog_parameter

The functionality is not used by anything yet, and the glUniform functions will
need to be reworked before this can reach its full usefulness.  It is
nonetheless a step towards integer support in the state tracker and classic drivers.
diff --git a/src/mesa/program/prog_execute.c b/src/mesa/program/prog_execute.c
index e7553c6..dbfd1b9 100644
--- a/src/mesa/program/prog_execute.c
+++ b/src/mesa/program/prog_execute.c
@@ -157,7 +157,7 @@
    case PROGRAM_NAMED_PARAM:
       if (reg >= (GLint) prog->Parameters->NumParameters)
          return ZeroVec;
-      return prog->Parameters->ParameterValues[reg];
+      return (GLfloat *) prog->Parameters->ParameterValues[reg];
 
    case PROGRAM_SYSTEM_VALUE:
       assert(reg < Elements(machine->SystemValues));