make boost-install refer to the correct target for installing the headers. Fixes #2416.

[SVN r49381]

Jamroot

@@ -490,7 +490,7 @@ alias build_all : libs/$(libraries)/build ;
 rule boost-install ( libraries * )
 {
     package.install install
-        : <dependency>/boost//install-headers $(install-requirements)
+        : <dependency>/boost//install-proper-headers $(install-requirements)
         : # No binaries
         : $(libraries)
         : # No headers, it is handled by the dependency.