In CAN_MCP2515.h the label MCP2515_RXM0 is defined twice. Once at line 158 and again at line 281. Nasty.
CAN Filters will not work in the prepared manor if setMask, setFilter and all the other helpers are defined private. MemFuncs writeAddress, setMode, readRXStatus, setMask, setFilter and readAddress at least should be public.
Now filters for std messages work - extened messages still don't get filtered/accepted.