Use @expose for Coordinate.z

By annotating the z property with @expose the compiler does not try to optimize that property in any way. See https://developers.google.com/closure/compiler/docs/js-for-compiler. The doc says that @expose should never be used in library code, but that's the only way I found for our case.
Merge pull request #435 from elemoine/coordinate-z

Use @expose for Coordinate.z
One direction pinch zoom
Increase touch zoom anim duration
Merge pull request #383 from elemoine/pinch-direction

One direction pinch zoom
Don't attempt to install PhantomJS on Windows

Instead, assume that phantomjs.exe is already in the user's path. It can
also be overridden on the build.py command line:

  build.py PHANTOMJS=path/to/phantomjs

or with an environment variable:

  set PHANTOMJS=path/to/phantomjs
  build.py
Merge pull request #441 from twpayne/dont-install-phantomjs-on-windows

Do not install PhamtomJS on Windows
Fix build/src/external/src/types.js dependency

The dependencies for build/src/external/src/types.js were wrong, which
meant that build/src/external/src/types.js would always be rebuilt,
which meant that almost everything else would be rebuilt too.
Merge pull request #442 from twpayne/fix-types-js-dependency

Fix build/src/external/src/types.js dependency
Only use glsl-unit if it is available
Merge pull request #443 from twpayne/only-use-glsl-unit-if-available

Only use glsl-unit if it is available