FIX:read_trans and write_trans

Ok, I have fixed read_trans and write_trans. To do this I based everything off of working with the files generated by the C code (as opposed to the ones in the mne-python sample data). Now write_trans will write files identical to mne_analyze. This will still work with the somewhat alien file in sample directory, but it ignores all the 'dig' stuff in that file. I have re-written the tests to exclude the 'dig' tests. I have also changed the code from creating an 'info' dictionary to a 'trans' dictionary.