Travis reduce package install cost
Travis reduce package install cost

1. Instead of installing libboost1.55-all-dev, which truly is everything
boost, just install the boost headers and the library components for the
very small number of non-header things we want.

2. Move the Linux package installation to be per-matrix-entry, this
allows us to customize by only installing the specific g++ version we
need, and exclude some boost components (using gcc >= 4.9 removes the
need for boost regex, for example).

This shaves several MINUTES of time from each test matrix entry, which
had been needlessly downloading and installing unneeded packages.

brechtvl/OpenShadingLanguage,gzorin/OpenShadingLanguage,gzorin/OpenShadingLanguage,brechtvl/OpenShadingLanguage,aconty/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,brechtvl/OpenShadingLanguage,lgritz/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,aconty/OpenShadingLanguage,imageworks/OpenShadingLanguage,lgritz/OpenShadingLanguage,imageworks/OpenShadingLanguage,gzorin/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,lgritz/OpenShadingLanguage,gzorin/OpenShadingLanguage,gzorin/OpenShadingLanguage,amartinez-cg/OpenShadingLanguage,imageworks/OpenShadingLanguage,brechtvl/OpenShadingLanguage,imageworks/OpenShadingLanguage,brechtvl/OpenShadingLanguage,aconty/OpenShadingLanguage,imageworks/OpenShadingLanguage,aconty/OpenShadingLanguage,lgritz/OpenShadingLanguage,lgritz/OpenShadingLanguage,aconty/OpenShadingLanguage