BUG: mseed, avoid pointer out of bound access

see #678
correcting type in readMSEEDBuffer

and refactoring, see #678
mseed: more verbosity, correcting reclen, tests

It was not possible specifying usefull reclens, trying to correct.

Adding tests related to see #678.

Adding more explicit logging to obspy-readbuffer.c to ease future
debugging, e.g.:
```
python -c "from obspy import read; read('/path/to/test.mseed', verbose=2)"

readMSEEDBuffer(): calling msr_parse with mseed+offset=58461152+0, buflen=8192, reclen=-1, dataflag=0, verbose=2
(null): Unpacking Steim-2 data frames
readMSEEDBuffer(): calling msr_parse with mseed+offset=58461152+4096, buflen=8192, reclen=-1, dataflag=0, verbose=2
(null): Unpacking Steim-2 data frames
```
Merge pull request #678 from mbyt/678

test_full_seed_with_non_default_dataquality failing with strange behavior