Exclude pipeline_mosaic test when built w/o Python

The pipeline file `pipeline/mosaic.xml` includes a filters.programmable,
which depends on Python. This patch excludes the test when we are not
built with Python.
fixups related to the big change in acbellgithub's 24828059066a77f56be6bec002a605c5d95af266
more cleanups for 24828059066a77f56be6bec002a605c5d95af266 for filters.hexbin
more fixups to filters.hexbin for 24828059066a77f56be6bec002a605c5d95af266
Merge branch 'master' of github.com:PDAL/PDAL
Rename 'pdal query' to 'pdal diff' and add some simple
XYZ delta statistics for default output #273
Add word expansion (shell syntax handling) for filenames in pipelines on
non-Windows systems.
Use some C++11 and use the boost::property_tree namespace to simplify code
in Options.*
Merge pull request #276 from PDAL/issues/272-rel-filenames

Add word expansion (shell syntax handling) for filenames in pipelines on
Merge pull request #274 from gadomski/pipeline-mosaic-without-python

Exclude pipeline_mosaic test when built w/o Python
Fix point count in las iterators.
Merge pull request #279 from PDAL/fixup

Fix point count in las iterators.
Merge branch 'master' into affine-filter