Robustify Boost.Book a little more. Don't register generators unless

'init' rule is called, so that we don't get into half-initialized state.

Revert previous change to doxygen.jam, since importing boostbook now is
harmless.


[SVN r21957]

tools/build

@@ -1 +1 @@
-Subproject commit fb8f4d64ee2b816d25a10a25b4b0d4e252d644bd
+Subproject commit d1cda1623c7fba3465c9f0e769652903c561056d