Speedup mchedr test.

- Read the mchedr catalog file only once (using setUpClass());
- Write QuakeML file only once.
test_mchedr: alt approach compatible with py2.6

...but uglier!
Reduce the number of phases in mchedr.dat

In order to sppedup test_mchedr.py
Merge pull request #693 from claudiodsf/speedup_pde_test

Speedup mchedr test.