* modules/access/dvb: Major rewrite of the code.

* modules/access/dvb: Major rewrite of the code.
  - new options (now prepended with --dvb) :
     --dvb-program : to work around the non-working --program
     --dvb-inversion : to (optionally) specify the inversion, which is not
                       the same as polarization
     --dvb-budget-mode : if you have a budget card this will set a filter
                         on 0x2000, meaning all PIDs will be returned by
                         the driver. The budget-mode is compatible with demux2.
     --dvb-satno : to specify a sat number in the diseqc system
     --dvb-voltage : to specify the voltage of the LNB (0 is a permitted
                     value in special configurations)
     --dvb-tone : to enable/disable the 22kHz tone (by default it is sent
                  if frequency >= lnb-slof)
  - fixed a handful of QPSK tuning bugs, especially the diseqc was not
    working and frequencies above 11700 couldn't be tuned to.
  - the modules now uses the inherited object variables for its
    configuration.
  - symbol-rate= url option is now srate= for consistency with the
    configuration variable.
  - all linux-dvb specific code is now in linux_dvb.c. access.c contains
    only code which could be reused on other platforms.
  - better keep track of demux file descriptors (especially useful on
    limited boards).
  - do not block in read() when no data is available.
  - fixed msleep() calls (reminder : mtime_t is in _microseconds_).

I didn't test the QAM and OFDM variants, so please report.