.SECONDARY should recognize pattern 'dependencies'

[Britton Kerin]

I want to be able to say something like this:

     .SECONDARY: %_openscad_poly
     %_openscad_poly: stl_outline_2_openscad_poly.perl %_profile.stl
             ./$+ >$@

so that make will always leave my generated intermediate file around.
But this doesn't seem to work, so I have to either name all the
%_openscad_poly
files explicitly, or use .PRECIOUS: which does more than I want (since I
always
use .DELETE_ON_ERROR:).

Britton