[phobos] isClass!T

[Lars Tandle Kyllingstad]

Several places in Phobos I've noticed tests like if(is(T==class)) that
check whether T is a class type.  I suspect it is usually meant for
these tests to pass if T is an interface as well, but this is not the
case.  Doing

  grep 'is(\w\+\s*==\s*class)' *.d

on the Phobos sources reveals many cases where the test for
is(T==interface) has most likely been forgotten.  This should be fixed,
and I think the best way is to add the following to std.traits:

  template isClass(T)
  {
      enum isClass = is(T == class) || is(T == interface);
  }

Most instances of is(T==class) in Phobos can then be replaced with
isClass!T.

What say you?

-Lars