PATCH: Sort SX vars

[Jesse Weinstein]

I found safe_strcmp in qofutil.h -- but it's not at all clear to me how
or whether I can or should #include that into gnc-sx-instance-model.c
where my patch touches. Advise?  As for having using a utf8-aware
comparison -- I'm open to suggestions, but, I'm not aware of what if any
is already in use, and I'm not sure it's necessary -- as I'm not sure
that the SX var subsystem can handle non-ASCII yet, either...

Jesse Weinstein