Add Jamfile to build PDF versions of all the docs.

Tweaked some existing Jamfiles so that PDF build finds all the necessary image files etc.
Tweaked fo.xsl to provide more options by default, and improve formatting.

[SVN r51104]

doc/Jamfile.v2

@@ -8,7 +8,7 @@ path-constant admonishment_location : ../../../../doc/src/images ;
 
 xml unordered : unordered.qbk ;
 boostbook standalone : unordered :
-    <xsl:param>admon.graphics.path=images/
+    <format>html:<xsl:param>admon.graphics.path=images/
     <xsl:param>navig.graphics.path=images/
     <xsl:param>html.stylesheet=boostbook.css
     <xsl:param>boost.root=../../../..