Increase MSVC warning level to 4.

There are some exceptions, a subset of the exceptions used by Chromium. They didn't seem to be useful warnings.

In code which we don't change much, like the preprocessor, I just suppressed the warnings in the specific files rather than changing the code.

There should be no functional changes in this patch.
Review URL: https://codereview.appspot.com/5570066

git-svn-id: https://angleproject.googlecode.com/svn/trunk@964 736b8ea6-26fd-11df-bfd4-992fa37f6226
diff --git a/src/compiler/ConstantUnion.h b/src/compiler/ConstantUnion.h
index d28a11b..fd9d94d 100644
--- a/src/compiler/ConstantUnion.h
+++ b/src/compiler/ConstantUnion.h
@@ -11,6 +11,10 @@
 
 class ConstantUnion {
 public:
+    ConstantUnion()
+    {
+        iConst = 0;
+    }
 
     POOL_ALLOCATOR_NEW_DELETE(GlobalPoolAllocator)        
     void setIConst(int i) {iConst = i; type = EbtInt; }
@@ -54,8 +58,6 @@
         default:
             return false;
         }
-
-        return false;
     }
 
     bool operator!=(const int i) const
@@ -89,8 +91,6 @@
         default:
             return false;   // Invalid operation, handled at semantic analysis
         }
-
-        return false;
     }
 
     bool operator<(const ConstantUnion& constant) const
@@ -104,8 +104,6 @@
         default:
             return false;   // Invalid operation, handled at semantic analysis
         }
-
-        return false;
     }
 
     ConstantUnion operator+(const ConstantUnion& constant) const