
1.  Add a 'flatten' argument to PostScriptTrace() so that can turn
    off path flattening and record curves as curves in RGML file
    (e.g., for systems that can draw curves, e.g., R in the future!).

2.  Bug in PostScriptTrace():  if PostScript image defines a path
    then does 'fill stroke' to fill the path then stroke it, the
    second path in the RGML file is empty (because PostScriptTrace()
    inserts a 'newpath').  A fix must NOT just remove the 'newpath'
    because otherwise separate paths just accumulate (e.g., the
    conversion of tiger.ps goes mental).

3.  Add tests/ code to check that PostScriptTrace() generates
    RGML code that is consistent with inst/dtd/rgml.dtd

4.  Allow assigning to subsets of picture objects.

5.  Export bitmaps from PostScript files too.  Requires modifying
    the PostScript code that translates the original file, extending
    RGML to store bitmaps, extending the Picture class to allow 
    bitmap elements, and code to render these bitmaps.

6.  Allow subsetting picture paths by *name* (requires naming
    picture paths).

