Merge unordered and hash from trunk.

- Only use Visual C++ pragma with appropriate compilers.
- Working link for Thomas Wang's hash function.
- Updated unordered rationale.
- Fix `unnecessary_copy_tests` for Visual C++ 12.
- Some extra insert tests.


[SVN r86728]

hash/doc/rationale.qbk

@@ -34,7 +34,7 @@ For other use cases, if you do need a higher quality hash function,
 then neither the standard hash function or `boost::hash` are appropriate.
 There are several options
 available. One is to use a second hash on the output of this hash
-function, such as [@http://www.concentric.net/~ttwang/tech/inthash.htm
+function, such as [@http://web.archive.org/web/20121102023700/http://www.concentric.net/~Ttwang/tech/inthash.htm
 Thomas Wang's hash function]. This this may not work as
 well as a hash algorithm tailored for the input.