Merge PDF build changes from Trunk.

[SVN r51417]

doc/Jamfile.v2

@@ -12,6 +12,8 @@
 
 import quickbook ;
 
+path-constant images : html ;
+
 xml optional
     :
         optional.qbk
@@ -26,5 +28,8 @@ boostbook standalone
         <xsl:param>toc.max.depth=2
         <xsl:param>toc.section.depth=2
         <xsl:param>chunk.section.depth=1
+        <format>pdf:<xsl:param>img.src.path=$(images)/
+        <format>pdf:<xsl:param>boost.url.prefix=http://www.boost.org/doc/libs/release/libs/optional/doc/html
     ;
 
+