* app/appenv.h: added a G_PI_2

* app/brush_header.h
* app/pattern_header.h: prefixed each FILE_VERSION with
G{BRUSH,PATTERN} to avoid namespace collision

* app/patterns.c: reflect above change

* app/iscissors.[ch]: merged in Austin's iscissors rewrite.. still
unfinished, but it's not like the old one did anything useful
anyway ;)

-Yosh