Merge from hash-predef.

.gitignore

@@ -1,4 +1,4 @@
-bin
+.bin
 boost-build.jam
 project-config.jam
 *.pyc

build.jam

@@ -37,7 +37,7 @@ project /boost/predef
 if [ project.is-jamroot-module $(__name__) ]
 {
     local attributes = [ project.attributes $(__name__) ] ;
-    $(attributes).set "build-dir" : bin ;
+    $(attributes).set "build-dir" : .bin ;
 }
 
 alias libs ;