A default ctor for Box is useful
Make Box.opIndex and .length usable by Stack.toHash
Fix Stack.extend
Correctly instantiate class types
Need to override toHash from Object

There is an interesting discussion of whether or not this should
be required here:
http://forum.dlang.org/thread/jtlj1k$1fdj$1@digitalmars.com

It looks like the idea was given up, at least for the time-being,
based on these recent commits:
https://github.com/D-Programming-Language/dmd/pull/1042
https://github.com/D-Programming-Language/druntime/pull/272
Fix Stack.opEquals
Temporarily disabling the toString code

There is a compiler regression that seems to be the cause of a
cryptic error message that is similar to the Appender error
message described in this post:
http://forum.dlang.org/thread/4D088C7F.5000300@digitalmars.com?page=3

See http://d.puremagic.com/issues/show_bug.cgi?id=10666
Fix the ctor mess

There is still a residual error that is the result of a compiler
implementation issue that does not distinguish between regular
and template constructors when matching their signatures.

The issue appears to be fixed and is waiting to be released
in DMD version 2.064

See http://d.puremagic.com/issues/show_bug.cgi?id=1528
and https://github.com/D-Programming-Language/dmd/pull/1409