Fix use of SortBy in csw.getrecords2
Create some tests for sorting
Use owslib.etree instead of lxml
Merge pull request #116 from mbertrand/sortby

Fix use of SortBy in csw.getrecords2
Tests should work with any of 3 xml library options
Merge pull request #117 from mbertrand/sortby

Tests should work with any of 3 xml library options