Continue error check improvements and write some docs.

Change-Id: I345b08490da21d9ee715ff1ddc80c1a816b579f4
diff --git a/graphics/java/android/renderscript/ProgramRaster.java b/graphics/java/android/renderscript/ProgramRaster.java
index 791dac8..5b55015 100644
--- a/graphics/java/android/renderscript/ProgramRaster.java
+++ b/graphics/java/android/renderscript/ProgramRaster.java
@@ -58,13 +58,13 @@
     void setLineWidth(float w) {
         mRS.validate();
         mLineWidth = w;
-        mRS.nProgramRasterSetLineWidth(mID, w);
+        mRS.nProgramRasterSetLineWidth(getID(), w);
     }
 
     void setCullMode(CullMode m) {
         mRS.validate();
         mCullMode = m;
-        mRS.nProgramRasterSetCullMode(mID, m.mID);
+        mRS.nProgramRasterSetCullMode(getID(), m.mID);
     }
 
     public static ProgramRaster CULL_BACK(RenderScript rs) {