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/libGLESv2/libGLESv2.cpp b/src/libGLESv2/libGLESv2.cpp
index e71ec28..73b7a2b 100644
--- a/src/libGLESv2/libGLESv2.cpp
+++ b/src/libGLESv2/libGLESv2.cpp
@@ -2980,7 +2980,11 @@
             {
                 attachmentObjectType = GL_TEXTURE;
             }
-            else UNREACHABLE();
+            else
+            {
+                UNREACHABLE();
+                return;
+            }
 
             switch (pname)
             {
@@ -3558,8 +3562,6 @@
     {
         return error(GL_OUT_OF_MEMORY, (GLubyte*)NULL);
     }
-
-    return NULL;
 }
 
 void __stdcall glGetTexParameterfv(GLenum target, GLenum pname, GLfloat* params)