Save about 3000 out of 28000 template instantiations in example/systems.cpp by replacing is_base_and_derived with integral constant members and inlining base_unit_converter_is_undefined

[SVN r46673]

libs/units

@@ -1 +1 @@
-Subproject commit b60f7d07b05a5ce4f04c01362426f27b0bc5b3e4
+Subproject commit 0919a7090a856461ecdf389f03ad3d6423029504