[Maxima] Ecl with defsystem

[Raymond Toy]

FWIW, I've checked in the changes to make maxima support building with
ecl and defsystem.

However, the actual build still uses asdf to build.  I hope someone
can test these changes to make sure I didn't break anything.  For some
reason, I cannot successfully build maxima with ecl using asdf.  (But
this isn't because of my changes; it didn't work before either.  Don't
know why.)

Also, I hope someone who builds maxima on Windows will try to build
maxima there using defsystem.  To make this work, you'll have to
modify src/Makefile.am and comment out the original rule for
binary-ecl/maxima and use the new (commented out) rule that uses
defsystem.  This works fine for me on Solaris and Mac OS X.

Please let me know if I've broken anything.

Ray