dvb/access.c - properly cast memory returned by malloc()

dvb/access.c - properly cast memory returned by malloc()
             - fix small memory leak on closing of dvb plugin.
dvb/linux-dvb.c - remove astray spaces
                - always empty the event queue before FE_SET_FRONTEND and FrontendCheck().
                  dvbstream does the same for OFDM and QAM.

Summary:
   DVB-C is working (did a few tests)
   DVB-T not tested.
   Using polarization=A doesn't work anymore INVERSION_AUTO is not honered for tuning.
   SEC_VOLTAGE_OFF is missing when using latest code DVB-1.1.7 from http://www.metzlerbros.org/dvb/index.html. While include/linux/dvb/version.h is not updated and still reflects this API version: #define DVB_API_VERSION 3