more lenient cuetimes parsing +rm cuetimes tests with missing files

Previously, we were expecting that the parser could deal with slightly
malformed timestamps, eg '00:9:43.000' (a single digit minute). More
recently, the parsing algorithm had changed to skip a cue if
timestamps in cuetimes are not absolutely perfect. This patch only
skips the cue if the timestamp is completely unrecognizable, or if the
error callback tells it to. This may or may not be desired behaviour,
I am not certain.

There is a small change to the lexer, so that the 'L_TIMESTAMP3' state
will not return a timestamp unless there is at least one digit
following the '.'. This way, we can return the EXPECTED_TIMESTAMP
rather than MALFORMED_TIMESTAMP error in cases where the milliseconds
component does not contain digits. This makes previously written tests
pass, so I'm okay with this.

There were a number of tests which were trying to load non-existent
files, and therefore failing. I've removed these tests because I can
not find the files anywhere. Perhaps they weren't needed (although I
expect they were). If anyone knows where these might be, it would be
helpful to know :>
removed 'cuetimes_unittest' from XFAIL_TESTS
Merge pull request #334 from caitp/cuetimes-fix

More lenient cuetimes parsing +rm cuetimes tests with missing files