Implement natural sorting so that our version number is correct.

setup.py

@@ -28,10 +28,53 @@
 ###############################################################################
 
 from setuptools import setup, find_packages
+import re
 
 VERSION_FILE = 'openlp/.version'
 
 try:
+    def natural_sort_key(s):
+        """
+        Return a tuple by which s is sorted.
+
+        ``s``
+            A string value from the list we want to sort.
+        """
+        def try_int(s):
+            """
+            Convert string s to an integer if possible. Fail silently and return
+            the string as-is if it isn't an integer.
+
+            ``s``
+            The string to try to convert.
+            """
+            try:
+                return int(s)
+            except:
+                return s
+        return map(try_int, re.findall(r'(\d+|\D+)', s))
+
+    def natural_compare(a, b):
+        """
+        Compare two strings naturally and return the result.
+
+        ``a``
+            A string to compare.
+
+        ``b``
+            A string to compare.
+        """
+        return cmp(natural_sort_key(a), natural_sort_key(b))
+
+    def natural_sort(seq, compare=natural_compare):
+        """
+        Returns a copy of seq, sorted by natural string sort.
+        """
+        import copy
+        temp = copy.copy(seq)
+        temp.sort(compare)
+        return temp
+
     from bzrlib.branch import Branch
     b = Branch.open_containing('.')[0]
     b.lock_read()
@@ -46,7 +89,8 @@ try:
         if revision_id in tags:
             version = u'%s' % tags[revision_id][0]
         else:
-            version = '%s-bzr%s' % (sorted(b.tags.get_tag_dict().keys())[-1], revno)
+            version = '%s-bzr%s' % \
+                (natural_sort(b.tags.get_tag_dict().keys())[-1], revno)
         ver_file = open(VERSION_FILE, u'w')
         ver_file.write(version)
         ver_file.close()