Slurping up Revision 1.25 of this document, which is described as:

"Rewrite the second on AnalysisUsage usage.  This documents the new
addRequiredTransitive member that Misha added, and explains the whole
concept a lot better.  Also, the document used incorrect "subsubsection"
tags instead of "doc_subsubsection" which this fixes."

llvm-svn: 12476