Fix label position in IE SVG renderer

[azuledu]

Label position in OL SVG renderer is set using the 'baseline-shift' property but this property does not work in IE as can be check here:
http://www.w3.org/Graphics/SVG/Test/20061213/htmlObjectHarness/full-text-align-02-b.html
As a workaround, the 'dy' property can be used to get a similar result. Explained here: http://nelsonslog.wordpress.com/2011/09/12/svgtext-baseline-considered-harmful/

[azuledu]

Example by @adube (Alexandre Dubé):
http://dev5.mapgears.com/tests/openlayers-ie9-label-shift/
Is reported in this thread:
http://lists.osgeo.org/pipermail//openlayers-users/2013-February/027420.html

[metteo]

The issue is also visible on ie11 (win7) with ol 2.12. Adding manually dy=".35em" (as in the commit) to tspan node in @adube's example helps (using ie dev tools) - this is the simplest case: single row labels.

EDIT: After debugging I noticed openlayers detects ie11 as mozilla so the commit won't work (it is still needed since the bug is still present in ie11). More info: http://blogs.msdn.com/b/ieinternals/archive/2013/09/21/internet-explorer-11-user-agent-string-ua-string-sniffing-compatibility-with-gecko-webkit.aspx

[sanak]

I fixed those issues in my forked branch (https://github.com/sanak/openlayers/tree/labels-IE-svg2)
and confirmed that it works correctly on IE11.
Could someone review my fix?
sanak@f0aebdd