Leave to SConscript files to decide default targets

SConstruct

@@ -175,4 +175,3 @@ env.Package(target = 'libucore-' + version_info['version_str'] + '.tar.gz',
             X_RPM_GROUP    = 'Development/Libraries'
 )
 
-env.Default('src')

src/SConscript

@@ -21,3 +21,5 @@ ucore_env.Alias('install',
     ucore_env.Install(os.path.join(prefix, 'lib'), [ucore_staticlib]))
 ucore_env.Alias('install', 
     ucore_env.InstallVersionedLib(os.path.join(prefix, 'lib'), [ucore_sharedlib]))
+
+ucore_env.Default([ucore_staticlib, ucore_sharedlib])

test/SConscript

@@ -32,4 +32,4 @@ cmd  = test_env.Command(target='test_phony' ,
                             action= test_env.Dir('.').abspath + '/' + test_executable)
 test_env.Depends(cmd, prog)
 test_env.AlwaysBuild(cmd)
-
+test_env.Default(test_executable)