fix usage of configure.get-relevant-features (#375)

The rule was misnamed, as it returned relevant properties,  not
features. The misnomer seems to had been the source of misuse: ac module
did not consider any feature other than <link> to be relevant when
checking for library existance. That could result in incorrect config
checks.

The change renames the rule to get-relevant-properties, and adds back
get-relevant-features that returns features. In addition, it fixes the
usage of get-relevant-features in ac module (it called the rule without
arguments), and removes another usage where its invocation could not
result in anything meaningful.

src/build/ac.jam

@@ -226,7 +226,9 @@ class ac-library : basic-target
                 library-path ?= [ os.environ $(name:U)_LIBPATH ] ;
             }
 
-            local relevant = [ property.select [ configure.get-relevant-features ] <link> :
+            local relevant = [ configure.get-relevant-features
+                [ $(property-set).raw ] ] ;
+            relevant = [ property.select $(relevant) <link> :
                 [ $(property-set).raw ] ] ;
             local min = [ property.as-path [ SORT [ feature.minimize $(relevant) ] ] ] ;
 
@@ -321,6 +323,5 @@ rule check-library ( target : true-properties * : false-properties * )
         $(true-properties) : $(false-properties) ] ;
     return <conditional>@$(instance).check
         [ property.evaluate-conditional-relevance
-            $(true-properties) $(false-properties)
-          : [ configure.get-relevant-features ] <link> ] ;
+            $(true-properties) $(false-properties) : <link> ] ;
 }

src/build/configure.jam

@@ -428,7 +428,7 @@ rule find-builds-raw ( project : ps : what : * )
     }
 }
 
-rule get-relevant-features ( properties * )
+rule get-relevant-properties ( properties * )
 {
     local ps-full = [ property-set.create $(properties) ] ;
     local ps-base = [ property-set.create [ $(ps-full).base ] ] ;
@@ -439,9 +439,15 @@ rule get-relevant-features ( properties * )
     return [ $(ps-relevant).raw ] ;
 }
 
+rule get-relevant-features ( properties * )
+{
+    local props = [ get-relevant-properties $(properties) ] ;
+    return $(props:G) ;
+}
+
 rule builds ( metatarget-reference : properties * : what ? : retry ? )
 {
-    local relevant = [ get-relevant-features $(properties) ] ;
+    local relevant = [ get-relevant-properties $(properties) ] ;
     local ps = [ property-set.create $(relevant) ] ;
     local t = [ targets.current ] ;
     local p = [ $(t).project ] ;
@@ -459,7 +465,7 @@ rule builds ( metatarget-reference : properties * : what ? : retry ? )
 
 rule find-builds ( what : properties * : * )
 {
-    local relevant = [ get-relevant-features $(properties) ] ;
+    local relevant = [ get-relevant-properties $(properties) ] ;
     local ps = [ property-set.create $(relevant) ] ;
     local t = [ targets.current ] ;
     local p = [ $(t).project ] ;