Implement the compile time checks for hash functions as a function instead of a templated class. Hopefully it will work on more compilers.

[SVN r28053]

libs/functional

@@ -1 +1 @@
-Subproject commit 2000b1aed886a9f995eb6388402d5602b01b1643
+Subproject commit f102d684cf51ab48936a5f1aca87c4efa242bdaa