Fix blksize (iosize) to report correctly, to handle bug with DB implementations
including firefox.
Add handler for F_RDADVISE although it currently does nothing.
Use 10.8 SDK for building OS X 10.8 kext

OS X 10.8 cannot load kexts built with 10.9 SDK.
Remove redundant kernel source directory checks.
Merge branch 'master' into zfsbundle