Build `timezone` module under `build` directory.

Instead of building the `timezone` module in the root directory, it is
now built as a sub-directory of the `build` directory. It must be named
timezone so that the `loaded.js` module works correctly.
Fix Travis CI minified source tests.

The Travis CI test of the minified source was failing because the
minification step had not been updated to reflect the new location of
the `timezone.js` source file.
Auto-generating `Makefile` timezone targets.

Updated the `Makefile` to auto-generate timezone data module target
names. The `util/tz2deps.js` program extracts the zone names from one or
more IANA timezone database file and outputs a single `Makefile`
variable definition. This is redirected to a `build/Makefile.deps` file
that is included in the `Makefile`. The `Makefile` then defines the
timezone modules names using the zone names.

GNU `make` will build and rebuild `build/Makefile.deps` when it is out
of date. See the **The GNU `make include` Directive** section of
[Advanced Auto-Dependency
Generation](http://make.paulandlesley.org/autodep.html) for details.