Comment typo corrected.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86562 b8fc166d-592f-0410-95f2-cb63ce0dd405
Stylistic change - jam construct like 'if $(var)-is-not-empty' does not actually test whether the $(var) variable is not empty and instead tests whether the variable is defined at all to any value. Specifically, if the variable is defined as an empty string, the test will still pass.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86565 b8fc166d-592f-0410-95f2-cb63ce0dd405
Minor stylistic line wrapping changes.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86566 b8fc166d-592f-0410-95f2-cb63ce0dd405