utils: new macro WITH-CURRENT-SOURCE-FORM
utils: new macro WITH-CURRENT-SOURCE-FORM

This utility is intended to be used by macro writers to help
application programmers. It allows errors signaled during
macroexpansion to be associated with particular sub-forms of the whole
macro form. This information can be used by tools like SLIME to
highlight that sub-form when reporting the error.

slyrus/mcclim,slyrus/mcclim