Fixed logic of difference_type selection, which was completely wack. In the

process, added digit_traits<> to compute the number of digits in intmax_t even
when not supplied by numeric_limits<>.


[SVN r8747]

libs/detail

@@ -1 +1 @@
-Subproject commit 37d08acea167734a19332961e8987a223b06ca5c
+Subproject commit 4bfd4da65005c70ac90b632d771cd2d494fdf580