libppd 2.0b4

Adde cupstestppd functionality, Coverity scan and fixes, several other bug fixes

• Transfer CUPS' cupstestppd utility to ppdTest() library function
  The valuable tool got forgotten in the first place, now it is available as ppdTest() library function and testppdfile command line utility. The command line utility only gets installed with ./configure called with --enable-testppdfile argument.
• In auto-generated PPDs do not set RGB default on mono printers (CUPS Issue #614)
  When a PPD for a driverless printer is generated by the ppdCreatePPDFromIPP() function and the get-printer-attributes IPP response gives "print-color-mode-default=auto" the PPD's default setting for "ColorModel" is always "RGB", even on monochrome printers, which makes printing fail on most devices. Now we ignore the "print-color-mode-default" if set to "auto".
• ppdLoadAttributes(): Added NULL check for missing PPD PageSize default
  Some PPDs, even "everywhere" PPDs generated by CUPS for a driverless IPP printer do not have a valid default value for the default page size, like "Unknown". Added a NULL check to avoid a crash by such PPD files.
• Coverity check done by Zdenek Dohnal for the inclusion of libppd
  in Fedora and Red Hat. Zdenek has fixed all the issues: Missing free(), potential string overflows, ... Thanks a lot!
• testppd: String got freed too early
  In this test program run by make check a string was used after already gotten freed. Discovered via a compiler warning, but program could have actually crashed.
• configure.ac: Change deprecated AC_PROG_LIBTOOL for LT_INIT (PR #8)