Check definitions appear in dominator of use

Also address use and def of ID in same instruction
diff --git a/CHANGES b/CHANGES
index 0e76412..8e5ab77 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2,6 +2,8 @@
 
 v2016.2-dev 2016-07-19
  - Start v2016.2
+ - Validator is incomplete
+   - Checks ID use block is dominated by definition block
 
 v2016.1 2016-07-19
  - Fix https://github.com/KhronosGroup/SPIRV-Tools/issues/261