Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56010
Documentation part of the fix

The constants mentioned in JspFactory.getPageContext(..) belong to JspWriter. There are no such constants in PageContext.
Javadoc in JavaEE 7 (as referenced in bug 56010) has been updated.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1574004 13f79535-47bb-0310-9956-ffa450edef68