Freebayes 1.3.8 does not build

[feghalya]

Building Freebayes v1.3.8 from source seems impossible as it is.

Using meson build -Dprefer_system_deps=false fails because it expects a vcflib submodule, and meson build -Dprefer_system_deps=true fails as well because the fastahack and smithwaterman libraries are hard-coded to use submodules.

The only way meson build worked was cloning vcflib in contrib/ and running meson build -Dprefer_system_deps=false, but then meson test -C build/ would fail because it could not find IntervalTree.h. To solve this, I had to change IntervalTree.h back to ../intervaltree/IntervalTree.h in src/BedReader.h and src/BedReader.cpp.