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 pull request #275 from gadomski/exclude-pcl-test-cpp

Exclude PCLBlockFilterTest when building w/o PCL
fixups for de-stage'ification of iterators
use boost-latest ppa's to upgrade travis config
upgrade Vagrant to use boost 1.55 too
Merge branch 'master' into issues/260-las14-extra-bytes