fix blank newline in XML output

While working with vtkPhyloXMLTreeWriter, I noticed that it would
occasionally output blank lines.  This commit fixes this behavior,
resulting in a more concise output file.

Change-Id: I3bd848198ea299246c1ef4d1f4a6ccea515729bf
vtkXMLReader can now read from an input string

Extend this class so that it can read from either a file or a
string.

Change-Id: Ida093f0c4c44896ed59da96b8950e7ffa2b6351b
new class: vtkPhyloXMLTreeReader

This class allows us to read a PhyloXML file to generate a
vtkTree.  This commit also contains corresponding change to
vtkPhyloXMLTreeWriter.

Change-Id: Idd7a7a997e24f0c751ee51ee8e2e9eb4c9c05c7a
consolidate tests for PhyloXML

Combine PhyloXML reader & writer tests into a single test,
and make it more thorough.

Change-Id: Ibb32ece7de203269a8508cb06eee91d94706f197
silence unused parameter warning

Change-Id: I16387bcb7a1f5198f5394a203a0345332740a147
Merge topic 'PhyloXMLReader' into master

1b01fb88 silence unused parameter warning
8bc3c4d3 consolidate tests for PhyloXML
04711678 new class: vtkPhyloXMLTreeReader
e99683a0 vtkXMLReader can now read from an input string
2f042ba4 fix blank newline in XML output