new writer: vtkPhyloXMLTreeWriter

This new class allows us to output vtkTrees in the PhyloXML format.

Change-Id: I9d4f0baaea6c0eba4ebb92730777473cf7b67ecf
attempt to silence "possible loss of data" warning

Change-Id: I7d5f3a67cacf4f846efaac3f9782b97bf6294a1b
improve the thoroughness of TestPhyloXMLTreeWriter

This test now compares its output against a baseline .xml file.

Change-Id: I1e612a1375fc933947228cfa03f16a27aab3bca4
add baseline directory

Forgot to add the new Baseline directory for IO/Infovis tests.
Hopefully this fixes my failing TestPhyloXMLTreeWriter test.

Change-Id: I153e3b280b27888122d2c09d4eddc18362e6382d
get the baseline file's path from the command line

This is an improvement over our previous approach of constructing
the path to the baseilne file from the testing directory.

Change-Id: I2dc0e1354c381ff770475ff2ab7f561b0122e582
Merge topic 'phyloxml_tree_writer' into master

c71d9c21 get the baseline file's path from the command line
81534288 add baseline directory
bba7656c improve the thoroughness of TestPhyloXMLTreeWriter
2841e3d3 attempt to silence "possible loss of data" warning
c0ff488b new writer: vtkPhyloXMLTreeWriter