CMake: make sure python library is in 2.x series

When looking up the python libraries, if you don't specify a minimum
version, it can pull in the python 3 libraries if not installed. Since
things don't build with python 3, make sure to restrict to the 2.x series.
CMake: Fix case sensitivity of SWIG package

On case-sensitive file systems, the SWIG module is in all caps.
Merge pull request #253 from simonsonc/swig-casing

CMake: Fix case sensitivity of SWIG package
make sure to pass in chunk_size argument to writer
make sure to pass in chunk_size argument to writer
Merge pull request #252 from simonsonc/python-ver

CMake: make sure python library is in 2.x series
Make lots of stuff fit in 80 columns, since we're almost there already.
Remove the silly "const" in front of native types.
Use the std namespace in some cpp files.
Remove NOOP return statements at the end of functions.
Consolidate code where it make sense.
Make more stuff fit in 80 columns.
Remove dead code.
CMake: Fix building with separate build dir

When building the python SWIG bindings in a separate build dir,
the build needs the directory of the build include path to get
pdal/pdal_defines.h.
Merge pull request #254 from simonsonc/separate-build-dir

CMake: Fix building with separate build dir
Implement Python 3 support #256
Add 'pdal diff' utility #255
numPointsNeeded in PCLBlock should be updated by the number of points read, not the number remaining after filtering
Support reading PointBuffers that have no XYZ on them #123
Remove supportsIterator().  Never called.
Merge pull request #257 from PDAL/no-supports-iter

Remove supportsIterator().  Never called.
Add: splitter filter to generate spatially contiguous point buffers of fixed size
Merge pull request #258 from PDAL/filter-create-tiles-alt2

Add: splitter filter to generate spatially contiguous point buffers of fixed size
Begin using 'option' rather than 'set' for PDAL options

Options become slightly more concise (drops the 'CACHE BOOL') and
enables use of CMAKE_DEPENDENT_OPTION macro, which could be useful
for the GDAL/GeoTIFF/TIFF trio among others.
small cleanups to filters.tiler