Add support for multi-delivery system frontends

Typically frontends that handle both DVB-T and DVB-C. The delivery system
is guessed from the arguments, or may be specified with option -5.
Add support for DVB-T/S2 and ISDB multistream.

Generic multistream support was added in Linux 3.6 in commit 287cefd096b.

http://git.kernel.org/gitweb.cgi?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=287cefd096b

The way it is added it is backwards compatible with older kernels.

This patch implements mis support in DVBlast. Unfortunately I don't
have mis compatible hardware and a way to test it, so I'm posting
this patch as RFC and RFT.

If your frontend reports FE_CAN_MULTISTREAM (you have to use Linux 3.6
and higher) it'll be invaluable to test if multistream support is
working.