USB printer update

- bind to 7/1/2 alternate setting by default, to fix printing with HP
  LaserJet 1200 and 2200
- ioctls needed by the GPL user-mode IEEE 1284.4 driver which is part of
  the HP OfficeJet Linux driver (http://hpoj.sourceforge.net):
  - dynamic switching between 7/1/[123] alternate settings
  - sending HP vendor-specific channel-change-request to support
    memory card readers on HP PhotoSmart printers
  - inquire more information about the peripheral, including
    /proc/bus/usb/xx/yy linkage to get even more information
- fix apparent array overflow (by 1 entry) in usblp_probe when more than
  the maximum number of USB printers are connected
- for the 2.2 version, added MODULE_{INC,DEC}_USE_COUNT to prevent rmmoding
  of printer.o (and subsequent OOPSes) while a USB printer device is open
- cleaned up the code in a few places by consolidating duplicated code