[MLton] mlnlffigen is awesome (was: bootstrap problem)

[Stephen Weeks]

> Although, I could be convinced that having any explicit
> -mlb-path-map argument disables the implicit ~/.mlton/mlb-path-map
> would be good enough.

It looks like were all agreed on allowing multiple -mlb-path-map
arguments, with later definitions overriding earlier ones.  The
simplest semantics seems to me to be no special treatment of
"explicit" mlb-path arguments.  It's also easier to implement since we
can put the following two lines in bin/mlton-script.

	-mlb-path-map "$lib/mlb-path-map"			\
	-mlb-path-map "$HOME/.mlton/mlb-path-map"		\

Or, if we want to, we could drop the second line.

My point being that from the compiler's point of view, it simply gets
a list of files in which to look for path variables.  That's easy to
understand for both compiler and user.

As to whether to automatically include the $HOME/.mlton/mlb-path-map",
given this semantics, it seems best not to.  For any project of even
middling size, the overhead of putting an extra line in the Makefile
or in writing a script to add the extra arg seems exceedingly minor.