Updated documentation on empty/whole and unprotected operations, to take into account David Abrahams' comments.

[SVN r32109]

libs/numeric/interval

@@ -1 +1 @@
-Subproject commit 8f396b0f366645cb2166218410c9b44d1511246d
+Subproject commit 4edc3fae18df36c6323cb61f490b61e516e210a1