Add 'splitwindow' plugin to the build list of the Waf build system.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@2956 ea778897-0a13-0410-b9d1-a72fbfd435f5

wscript

@@ -324,6 +324,7 @@ def build(bld):
         build_plugin('export')
         build_plugin('filebrowser')
         build_plugin('htmlchars')
+        build_plugin('splitwindow')
         build_plugin('vcdiff')
 
     # Translations