simplified loop primitives

make +loop working with negative loop increments as tested by Hayes.


git-svn-id: svn://svn.code.sf.net/p/amforth/code/trunk@1660 fd1c0b69-5d68-47f5-910c-86182ebb6ecd
rewrite using Forth

git-svn-id: svn://svn.code.sf.net/p/amforth/code/trunk@1661 fd1c0b69-5d68-47f5-910c-86182ebb6ecd
Merge branch 'hq'