Removing space between buttons in Buttonset in Vector

Removing whitespace between buttons in jquery.ui.buttonset in vector skin.
jQuery UI Buttons are displayed inline-block. In case there is
whitespace between button nodes in the HTML source, the whitspace would
be also rendered. To avoid this, jQuery UI decided to put a negative
margin in place. However, this negative margin is not enough in Vector skin by
MediaWiki (see attached screenshots in bug 32687). By setting the margin
from -0.3em to -0.4em this issue will be addressed in all tested browsers.
Since the text and icons in the buttons have a padding around 1em, this
patch will not obscure text or icons in the buttons. The only downside
is the shadow that is multiplied below the button and thus darker. But
this was an issue before and it will be just more obvious after applying
this patch.

Bug: 32687
Change-Id: I2577fe0ed79f0704ff40c019ec824d8ba62c3bf1
Merge "Removing space between buttons in Buttonset in Vector"