MySQL compatibility: TIMESTAMPDIFF is now an alias for DATEDIFF.

h2/src/docsrc/help/help.csv

@@ -2941,12 +2941,13 @@ DATEADD('MONTH', 1, DATE '2001-01-31')
 "
 
 "Functions (Time and Date)","DATEDIFF","
-DATEDIFF(unitString, aTimestamp, bTimestamp)
+{ DATEDIFF | TIMESTAMPDIFF } (unitString, aTimestamp, bTimestamp)
 ","
 Returns the difference between two timestamps.
 This method returns a long.
 The string indicates the unit.
 The same units as in the EXTRACT function are supported.
+TIMESTAMPDIFF is supported for MySQL compatibility.
 ","
 DATEDIFF('YEAR', T1.CREATED, T2.CREATED)
 "