Add libopenthreads-dev to ubuntu-precise; resolves travis-ci/apt-package-whitelist#650
Add libopenthreads-dev to ubuntu-precise; resolves travis-ci/apt-package-whitelist#650

Packages: libopenthreads-dev libopenthreads20 libopenscenegraph-dev libopenscenegraph100 openscenegraph-doc openscenegraph openscenegraph-examples

jschlyter/apt-package-whitelist,rnestler/apt-package-whitelist,jschlyter/apt-package-whitelist,sternb0t/apt-package-whitelist,jmerkow/apt-package-whitelist,AlCutter/apt-package-whitelist,AlCutter/apt-package-whitelist,christophgysin/apt-package-whitelist,travis-ci/apt-package-whitelist,phw/apt-package-whitelist,Tyrael/apt-package-whitelist,christophgysin/apt-package-whitelist,rnestler/apt-package-whitelist,Tyrael/apt-package-whitelist,sternb0t/apt-package-whitelist,jmerkow/apt-package-whitelist,phw/apt-package-whitelist,travis-ci/apt-package-whitelist