next fix on our XMLHttpRequest implementation

git-svn-id: svn://svn.code.sf.net/p/htmlunit/code/trunk@8773 5f5364db-9458-4db8-a492-e30667be6df6
use a constant

git-svn-id: svn://svn.code.sf.net/p/htmlunit/code/trunk@8774 5f5364db-9458-4db8-a492-e30667be6df6