Try preventing static casts when calling hash_value.

[SVN r63716]

test/implicit_fail_test.cpp

@@ -0,0 +1,16 @@
+#include <boost/functional/hash.hpp>
+
+namespace test
+{
+    struct base {};
+    std::size_t hash_value(base const&) { return 0; }
+    
+    struct converts { operator base() const { return base(); } };
+}
+
+int main() {
+    boost::hash<test::converts> hash;
+    test::converts x;
+    
+    hash(x);
+}