boost: reference patch with issue reports.
boost: trunk now on github with submodules.

* Also remove legacy rpath handling logic, which is taken care of by
  install_name_tool.
boost: fix C++11 flags for trunk.

* Trunk now use "-x" flag to control which language to use, for instance
  "clang++ -x c" will be used to compile C code, while Homebrew will
  still think it is invoking the C++ compiler. It is easier to just set
  cxxflags and linkflags.
LD64Dependency: adjust initializer signature

The method signature of Dependency changed in
1fdf69b90382c43493a5f62f0020729289db6c70, however LD64Dependency was
missed in the update. This resulted in failures in merge_repeats(),
which creates many dependency objects using all three arguments.
libpng 1.6.10
ttfautohint 1.00
gdk-pixbuf 2.30.6
freetype: update revision
freetype: update 2.5.3 bottle.
cairo: update revision
cairo: update 1.12.16 bottle.
cairomm: update revision
cairomm: update 1.10.0 bottle.
Update revisions on bottled libpng dependents
ghostscript: update 9.10 bottle.
gd: update 2.1.0 bottle.
s-lang: update 2.2.4 bottle.
imagemagick: update 6.8.7-7 bottle.
graphviz: update 2.36.0 bottle.
Update revisions on libpng dependents