libdvdcss patches

[H}kan Hjort]

First change the error text in CSSTest, since dvd ioctls are always
compiled in now. Shoulw we keep the message or simply remove it all?

Second patch adds a small function that (for unix) stats the string
that we've been told to open, and trys to determin if we should bother
using the ioctls. I.e. they should only be use (tried) on actuall DVD
drives. Images and files on normal file systems doesn't need any
authentication and if they are encrypted one needs to crack the keys
anyway.
I'm not sure exactly what to test for here though, I compromised and
check for block or char devices on all systems. It lacks code for
widows as I don't have any clue what should be done there.
Perhaps this could/should be done as part of _dvdcss_open instead?