howto.html: Update.

2007-12-09  Benjamin Kosnik  <bkoz@redhat.com>

	* docs/html/ext/howto.html: Update.
	* docs/html/ext/sgiexts.html: Same.
	* docs/html/ext/concurrence.html: New. Document extensions.
	* docs/html/17_intro/api.html: Move some bits...
	* docs/html/17_intro/backwards_compatibility.html: here. New. Add
	compatibility suggestions, move existing ones.
	* docs/html/17_intro/howto.html: Update info.
	* docs/html/18_support/howto.html: Tweak.
	* docs/html/faq/index.html: Update thread info.
	* docs/html/documentation.html: Add links.
	* docs/html/20_util/allocator.html: Update info.
	* include/precompiled/stdc++.h: Add C++0x includes if appropriate.
	* testsuite/17_intro/headers/c++200x/all.cc: Same.

From-SVN: r130732