Make redo read byte-strings from the database.

By default, the database redo uses to store file state returns filenames
as Unicode strings, and if redo tries to run a build-script whose
fully-qualified path contains non-ASCII characters then redo crashes
when trying to promote the path to a Unicode string.

This patch ensures that the database always returns byte-strings, not
Unicode strings. That way, the fully-qualified path and the target name
are both byte-strings and can be joined without issue.

(Fixes a bug reported by Zoran Zaric.)

state.py

@@ -15,6 +15,7 @@ def _connect(dbfile):
     _db = sqlite3.connect(dbfile, timeout=TIMEOUT)
     _db.execute("pragma synchronous = off")
     _db.execute("pragma journal_mode = PERSIST")
+    _db.text_factory = str
     return _db