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/sampler.cpp b/src/mesa/program/sampler.cpp
index 1457d11..e8d34c6 100644
--- a/src/mesa/program/sampler.cpp
+++ b/src/mesa/program/sampler.cpp
@@ -132,6 +132,6 @@
 
    index += getname.offset;
 
-   return prog->Parameters->ParameterValues[index][0];
+   return prog->Parameters->ParameterValues[index][0].f;
 }
 }