Bug 1027095 - Convert XPathResult to WebIDL bindings - move files and rename class. r=bz.

--HG--
rename : dom/xslt/xpath/nsXPathResult.cpp => dom/xslt/xpath/XPathResult.cpp
rename : dom/xslt/xpath/nsXPathResult.h => dom/xslt/xpath/XPathResult.h
Bug 1027095 - Convert XPathResult to WebIDL bindings - add WebIDL API and switch. r=bz.