only use PUBLIC in PDAL_LINKAGE if CMake supports it, otherwise stick with LINK_PUBLIC
Exclude PCLBlockFilterTest when building w/o PCL

This patch puts filters/PCLBlockFilterTest.cpp inside a WITH_PCL check,
so we build with it only when we have PCL available.
Merge branch 'master' into issues/264-pdal-linkage
Add BPF files.
some more cleanups related to #285
Merge pull request #275 from gadomski/exclude-pcl-test-cpp

Exclude PCLBlockFilterTest when building w/o PCL
use boost-latest ppa's to upgrade travis config
upgrade Vagrant to use boost 1.55 too
Merge pull request #287 from abellgithub/bpf

Add BPF files.
Very simple decompression for BPF.
Add a sbet reader

Sbet is a simple binary format used to store inertial measurement unit
(IMU) data. These data include position and trajectory information.
Simplify some code in dimension.
Make things fit in 80 columns.
Merge pull request #293 from abellgithub/bpf

Very simple decompression for BPF.
turn off clang builds for now
Merge pull request #295 from abellgithub/dimension

Simplify some code in dimension.
Merge pull request #294 from gadomski/sbet-reader

Add a sbet reader
Merge pull request #297 from PDAL/issues/264-pdal-linkage

Use PUBLIC linkage only if CMake > 2.8.12, otherwise use LINK_PUBLIC
Add: PCL kernel for the PDAL app
Format cleanup and so on for scaling filter.
Allow point dump with sequential iterators.