Respect indentation at the start of a file.

Fix bug where a code block at the start of a file was not recognised.
I was actually adding this test to check that the `source_mode_unset`
mechanism in `doc_info_grammar.cpp` was working, but it ended exposing
this bug.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85590 b8fc166d-592f-0410-95f2-cb63ce0dd405
Example of building documentation outside of the boost tree.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85596 b8fc166d-592f-0410-95f2-cb63ce0dd405
Tweak the documentation structure.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85597 b8fc166d-592f-0410-95f2-cb63ce0dd405
Starting to document xsl parameters.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85598 b8fc166d-592f-0410-95f2-cb63ce0dd405
A little more about upgrading to 1.6

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85599 b8fc166d-592f-0410-95f2-cb63ce0dd405
Remove unnecessary include.

I moved the code that required this in [75264].

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85600 b8fc166d-592f-0410-95f2-cb63ce0dd405