Preprocessing xxxInfo.plist

[Nicola Pero]

While working with Rodolfo W. Zitellini on the Renaissance port of Ink, we
ended up with having 2 separate xxxInfo.plist - one for GNUstep and the
other one for Apple.

I thought it would be brilliant if we could merge them by supporting C
preprocessor conditionals in .plist, such as

 NSTypes = (
  {
    NSName = "rtf";
    NSHumanReadableName = "RTF Document";
    NSDOSExtensions = ("rtf");
    NSUnixExtensions = ("rtf");
    NSMIMETypes = ("text/rtf");
    NSDocumentClass = Document;
#ifdef GNUSTEP
    NSIcon = FileIcon_rtf.tiff;
#else /* APPLE */
    NSIcon = FileIcon_rtf.icns;
#endif
    NSRole = Editor;
  },
  
I thought it would be brilliant, so I did it - I implemented this in my
gnustep-make.  You can turn on support for this feature by setting

xxx_PREPROCESS_INFO_PLIST = yes

if you do, then you should supply a xxxInfo.cplist (instead of 
xxxInfo.plist).  gnustep-make automatically runs the C preprocessor as 
appropriate to build xxxInfo.plist from xxxInfo.cplist before using it.