increase the precision of constants

Summary: I have no idea why we were shortening these. I took the new version from ext/standard/php_math.h

Fixes #3529
@​tarjantest

Reviewed By: @paulbiss

Differential Revision: D1507921
Fix DOMText::split to not error on null object pointer

Summary: It tried to add an orphan even when no DomDocument was set. Also porting bug 52656.

Also add an alias to DOMText::isWhitespaceinElementContent
It was renamed to isElementContentWhitespace in the current wc3 recommendation
See http://www.w3.org/TR/DOM-Level-3-Core/core.html#Text3-isElementContentWhitespace

Closes https://github.com/facebook/hhvm/pull/3523

Reviewed By: @ptarjan

Differential Revision: D1506179