Use po directory either in current or parent folder

wscript

@@ -371,14 +371,19 @@ def set_options (opt):
 # Taken from Geany's wscript, modified to support LINGUAS variable
 def write_linguas_file (self):
     linguas = ''
+    # Depending on Waf version, getcwd() is different
+    if os.path.exists ('./po'):
+        podir = './po'
+    else:
+        podir = '../po'
     if 'LINGUAS' in Build.bld.env:
         linguas = Build.bld.env['LINGUAS']
     else:
-        files = os.listdir ('../po')
+        files = os.listdir (podir)
         for f in files:
             if f.endswith ('.po'):
                 linguas += '%s ' % f[:-3]
-    f = open ('../po/LINGUAS', 'w')
+    f = open (podir + '/LINGUAS', 'w')
     f.write ('# This file is autogenerated. Do not edit.\n%s\n' % linguas)
     f.close ()
 write_linguas_file = feature ('intltool_po')(write_linguas_file)