rather than piggy-back the perform-actions sexp on top of the when sexp, it works better to make it its own operator
(fixes Mantis #2956)

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10110 387891d4-d844-0410-90c0-e4c51a9137d3
clarify help... OP_AND will actually evaluate all arguments

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10111 387891d4-d844-0410-90c0-e4c51a9137d3