Renamed Boost.Build's internal assert.nonempty-variable() rule to assert.variable-non-empty().

[SVN r46257]

src/build/feature.jam

@@ -957,7 +957,7 @@ rule compress-subproperties ( properties * )
         if ! $(p:G)
         {
             # Expecting fully-gristed properties.
-            assert.nonempty-variable p:G ;
+            assert.variable-not-empty p:G ;
         }
 
         if ! subfeature in $($(p:G).attributes)

src/kernel/class.jam

@@ -279,7 +279,7 @@ local rule __test__ ( )
         rule invariant3 ( )
         {
             local v = 10 ;
-            assert.nonempty-variable v ;
+            assert.variable-not-empty v ;
         }
     }
 #    class derived1 : myclass ;

src/util/assert.jam

@@ -231,7 +231,7 @@ rule exact-equal ( a * : b * )
 
 # Assert that the given variable is not an empty list.
 #
-rule nonempty-variable ( name )
+rule variable-not-empty ( name )
 {
     local value = [ modules.peek [ CALLER_MODULE ] : $(name) ] ;
     if ! $(value)-is-not-empty