Add AudioFormat::AC3

It turns out the HD-PVR1 uses AC3 for its audio, so add it to the audio
formats enum.
Add MEDIASUBTYPE_DVM GUID definition

We're just going to use DVM to identify the AC3 format on the pin.
Add demuxer helper functions

These functions are used to create audio/video pins on demuxers.  Also
specifies the names of the demuxer pins.
Add DirectConnectFilters helper function

This function attempts to directly connect the output pins of an output
fitler to the input pins of an input filter automatically.  If any pins
were connected by the function, it returns true, otherwise false.

Does not use smart connect -- this function is meant to be used to
connect a crossbar filter to the main device filter.
Add MPEG-1 audio support

Apparently the HD-PVR Rocket uses MPEG-1 audio.
Remove 'trying pins' message

It's a bit redundant to have this message.  It happens for specific
devices regardless, so there's no real need to warn about it.
Set MediaTypePtr pointer value to null on clear

This prevents any potential of the pointer value being leaked if the
pointer value fails to be set
Fix HDevice::ConnectPins

The call to GetFilterPin has two things wrong with it:

First, it had the parameters in the wrong order.

Second, the if expression failed on success rather than on actual
failure from it.
Only add audio filter on graph if custom audio

The audio device filter is the same as the video device filter if it's
the video device's built-in audio.  Adding it twice to the graph is sort
of pointless and potentially problematic for all I know.
Add elgato support
Add support for HD-PVR 2, HD-PVR Rocket, and Roxio