Fix the way paths are adjusted for Cygwin

[SVN r27097]

v2/tools/testing.jam

@@ -278,17 +278,9 @@ rule run-path-setup ( target : source : properties * )
     {    
         dll-paths = [ sequence.transform path.native : $(dll-paths) ] ;
         
-        local var-name = LD_LIBRARY_PATH ;
-        # Even on cygwin, the LD_LIBRARY_PATH has no effect, need to
-        # use PATH. 
-        if [ os.on-windows ]
-        {
-            var-name = PATH ;
-        }
-        
         PATH_SETUP on $(target) = 
-          [ common.path-variable-setting-command $(var-name) 
-            : $(dll-paths) $$(var-name) : exported ] ;
+          [ common.prepend-path-variable-command
+              [ os.shared-library-path-variable ] : $(dll-paths) ] ;
     }            
 }