* Add a new document-specific variable, HAS_INDEX, to specify if a
given document is marked up with <indexterm> entries.
* Rework the index support so that both HAS_INDEX and GEN_INDEX are
checked before trying to generate an index for a document.
* Only create index.sgml if both HAS_INDEX and GEN_INDEX are set.
This allows us to recursively build the documentation tree with
GEN_INDEX=1 and have it only try to create an index (very time
consuming) for the few documents that are ready for this. Previously,
running "make GEN_INDEX=1" from the top of the doc tree would look for
index terms in every single document.
With this, I hope we can start building our docs with GEN_INDEX set on
freefall so that users browsing the HTML docs will get the benefit of
the index we've been hiding in CVS for 6 months.
* Add chapter on kernel debugging (repo-copied from the Handbook)
* Change "Introduction" part with 4 empty chapters to a
"Introduction" chapter with 4 mostly empty <sect1>s.
* Combine many of the different <part>s that contain only one empty
<chapter> into larger <part>s.
* Add * in front of unfinished chapter names so its very clear what
needs to be worked on.
* Added some <filename> tags where appropriate.
