FIX bug related to loading datablocks.

datablocks can have a length different than the sampling frequency. The current code assumes that the sampling frequency and the number of samples per block are the same. This turns out to be a bad assumption.

addresses issue: https://github.com/mne-tools/mne-python/issues/1324

@herrlich10 or someone else, could you test this to see if this resolves the issue. I would do so but my Matlab is not compatible with the beta Yosemite I installed (a bit impulsively).