Py3k: fixing core waveform plugins segy test

segy files with empty tr.stats.segy were incorrect
Py3k: fixing core waveform plugins sacxy test

readline() seems to behave different when used for stripping newlines.
Therefore, reading the line manually and then parsing the data from the
string.
Py3k: fixing more core tests

* doctests
* native_str for scipy window
* putting utf-8 back to beginning of files