Updates for v0.50:
Moved much of the PPD-import logic into a shared function.
Automatically reimport previously-imported PPDs when updating to a new version of a known PostScript driver.
Ask if the user wants to update the active copy of a driver when the repository version is updated.
Fixed error in locating cupswiz.exe when the desktop object doesn't exist.
Fixed broken update of PRDESC.LST when upgrading to a new version of a known PostScript driver.