Add support for target visibility, use for dist, test, install

This means we can no longer write:

install = false

Now it should be:

*: install = false

1 files changed, 5 insertions, 2 deletions

diff --git a/build2/dist/init.cxx b/build2/dist/init.cxx
index 338f6c8..2bf26e0 100644
--- a/build2/dist/init.cxx
+++ b/build2/dist/init.cxx
@@ -49,8 +49,11 @@ namespace build2
         v.insert<path>         ("dist.cmd");
         v.insert<strings>      ("dist.archives");
 
-        v.insert<bool>         ("dist");         // Flag.
-        v.insert<string>       ("dist.package"); // Project's package name.
+        v.insert<bool> ("dist", variable_visibility::target); // Flag.
+
+        // Project's package name.
+        //
+        v.insert<string> ("dist.package", variable_visibility::project);
       }
     }