Building with latest changes in Git -- and other news

[John Mandereau]

Hi,

If you encounter 'make web' failure, please delete
buildscripts/langdefs.pyc from the source tree and try again.  This
operation has to be repeated in all source trees used for building which
include commit f7732c9a7e6ad2bd3f91dc39201e8249cfc82065
"Move langdefs.py to python, and clean up doc building scripts".

Although I've made a clean build, I might not have catched all important
details and nitpicks in the lot of changes I made to clean up and fix
doc building, so please expect to encounter breakage, inconcistency...
and hopefully a bunch of fixed images and links to lys.

I've also added --latex option to lilypond-book, as it was requested
some time ago to bug-lilypond.

Cheers,
John