Added support for UTC date time labels.

  * dygraph-utils.js:
    new utc switch parameter for `Dygraph.dateString_`
    and new signature for `Dygraph.hhmmss_`.

  * dygraph.js:
    support for UTC date time labels in date formatter.
    Also rename it to `dateAxisLabelFormatter`  for homogeneity
    with the numeric one. and add  a `dateValueFormatter`.

  * dygraph-options-reference.js:
    new `labelsDateUTC` option.
Added support for option `labelsDateUTC` to the date tick picker.

    * dygraph-tickers.js:
      simplified date tick generation. `Dygraph.getDateAxis`
      now produces nice ticks both in UTC and local time.

    * dygraph-utils.js:
      removed `Dygraph.dateSetters` and `Dygraph.setDateSameTZ`
      because they are not needed any more.
Format year of monthly tick lables with 2 digits instead of 4.

Since commit 7b2dfd0 (Oct 15, 2013) the format of monthly tick
labels is `%b %Y` (e.g. Oct 2013). Before the format was '%b %y'
(e.g. Oct 13). Revert to the later format because it seems to be
an accidental change.

  * `dygraph.js`:
    Revert format of monthly tick labels from `%b %Y` to `%b %y`.
Insignificant fix of `>` in jsdoc comments.
Added UTC date label tests and adapted existing ones.

    * tests/labelsDateUTC.html:
      New test/demo for the option  `labelsDateUTC`.
      Display several days of data according to UTC and to local time,
      and compare the tick placement and the label format.

    * tests/x-axis-formatter.html:
      Added `opts` argument to `axisLabelFormatter` function
      (used by inner `Dygraphs.dateAxisLabelFormatter` call).
Added automated test for UTC date ticks and labels.

The date tick tests are broken in the ticker automatic test suite
because they assume EST timezone. In addition, the suite is disabled.
Fix the  automatic test suite for the case UTC ticks and labels:

  * `auto_tests/tests/date_ticker.js`:
    Test the generation of ticks and labels at nice time positions
    according to UTC as set by option `labelsDateUTC`.
    Include the date axis tests from `auto-tests/tests/tickers.js-disabled`
    with the required changes of timestamps and with initial ticks
    out of range removed.
Removed disabled ticker test suite (no longer needed).

The tickers test suite is disabled. In addition, most tests there are broken.
Date ticker tests are fixed and moved to a separated date ticker test suite
by last commit. Hence move numeric ticker tests to the numeric ticker
test-suite and remove the disabled tickers test-suite.

  * `auto_tests/tests/numeric_ticker.js`:
    Include tests from `auto_tests/tests/tickers.disabled-js`
    but commented because they are all broken.

  * auto_tests/tests/tickers.disabled-js:
    Delete it because it is no longer needed.
Bug fix for horizontal scrolling on hidpi devices
Add panning interaction model functions to dygraph-externs

Add the startPan(), movePan(), and endPan() functions to the externs file. These functions are commonly used when defining custom interaction models and must be defined in order to satisfy the closure compiler.
Add Dygraph.PointType to dygraph-types

Add the Dygraph.PointType type to the dygraph-types externs file. This type is used when defining a clickCallback function and must be defined in order to satisfy the Google Closure compiler.
Merge pull request #305 from brentwalther/master

Add panning functions to dygraph-externs and PointType to dygraph-types
Merge pull request #303 from danvk/fix-hidpi

Fix HiDPI over-scrolling issue
Replace '&nbsp;' with '&#160;', so that the legend works in XHTML pages as well
Merge pull request #308 from yankee42/fixXmlEntities

Replace '&nbsp;' with '&#160;', so that the legend works in XHTML pages
Update the hidpi test to work on a wider variety of platforms (e.g. when running the tests via `java -jar ./auto_tests/lib/JsTestDriver-1.3.3c.jar --tests all`)
Merge pull request #309 from hulkholden/hidpi

Update the hidpi test to work on a wider variety of platforms
Add missing license text to dygraph-externs.js and dygraph-types.js
Merge pull request #310 from hulkholden/license

Add missing license text to dygraph-externs.js and dygraph-types.js
Changed code to separate graph stacking logic by axis.
Merge branch 'CSG/MultiAxis-StackedGraph' into CSG-v1.0.1