Merge branch 'add-already-loaded-systems-doc' into 'master'

@c FIXME: the following is too complicated for here, especially since

@c :force hasn't been defined yet.  Move it. [2014/02/27:rpg]

@findex already-loaded-systems

@defun load-system system @Arest{} keys @Akey{} force force-not verbose version @AallowOtherKeys{}

Apply @code{operate} with the operation @code{load-op}, the

@var{system}, and any provided keyword arguments.  Calling

it's an explicitly requested system or the dependencies thereof).

@end defun

@defun already-loaded-systems

Returns a list of names of the systems that have been successfully

loaded so far.

@end defun

@node Moving on,  , Convenience Functions, Using ASDF

@section Moving on