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.)

t/test.do

@@ -3,4 +3,5 @@ redo-ifchange all
 redo nonshelltest shelltest \
 	deltest deltest2 test.args test2.args passfailtest chdirtest \
 	curse/test deps/test "space dir/test" modetest makedir2 \
-	silencetest touchtest stamp/test alwaystest ifcreate-test
+	silencetest touchtest stamp/test alwaystest ifcreate-test \
+	unicode

t/unicode.do

@@ -0,0 +1,2 @@
+# Test that redo can handle a script whose path contains non-ASCII characters.
+redo test-uniçøðë/test1