Fix the following warning:

/var/lib/python-support/python2.5/jack_functions.py:243: Warning: 'with' will become a reserved keyword in Python 2.6
/var/lib/python-support/python2.5/jack_functions.py:245: Warning: 'with' will become a reserved keyword in Python 2.6
/var/lib/python-support/python2.5/jack_functions.py:245: Warning: 'with' will become a reserved keyword in Python 2.6

--- a/jack_functions.py	2007-10-20 12:24:55.000000000 +0200
+++ b/jack_functions.py	2007-10-20 12:25:24.000000000 +0200
@@ -240,9 +240,9 @@
     ff = blocks % CDDA_BLOCKS_PER_SECOND
     return mm, ss, ff, blocks
 
-def starts_with(str, with):
-    "checks whether str starts with with"
-    return str[0:len(with)] == with
+def starts_with(str, x):
+    "checks whether str starts with a given string x"
+    return str[0:len(x)] == x
 
 ## #XXX the following will be used if all references to it have been updated.
 ## meanwhile the wrapper below is used.