Use Versioned to ensure SourceStamps have the right types

Since SourceStamps are used against the DB, types matter, so this patch
uses styles.Versioned to coerce branch, revision, and patch to the
correct type.

buildbot/sourcestamp.py

@@ -1,9 +1,10 @@
 # -*- test-case-name: buildbot.test.test_sourcestamp -*-
 
 from zope.interface import implements
+from twisted.persisted import styles
 from buildbot import util, interfaces
 
-class SourceStamp(util.ComparableMixin):
+class SourceStamp(util.ComparableMixin, styles.Versioned):
     """This is a tuple of (branch, revision, patchspec, changes).
 
     C{branch} is always valid, although it may be None to let the Source
@@ -23,6 +24,8 @@ class SourceStamp(util.ComparableMixin):
        and all must be on the same branch.
     """
 
+    persistenceVersion = 1
+
     # all four of these are publically visible attributes
     branch = None
     revision = None
@@ -140,4 +143,14 @@ def asDict(self):
         result['changes'] = [c.asDict() for c in getattr(self, 'changes', [])]
         return result
 
+    def upgradeToVersion1(self):
+        # version 0 was untyped; in version 1 and later, types matter.
+        print "upgrading sourcestamp to version 1"
+        if self.branch is not None and not isinstance(self.branch, str):
+            self.branch = str(self.branch)
+        if self.revision is not None and not isinstance(self.revision, str):
+            self.revision = str(self.revision)
+        if self.patch is not None and not isinstance(self.patch, str):
+            self.patch = str(self.patch)
+
 # vim: set ts=4 sts=4 sw=4 et: