FIX: removed 10% chance of parseISODate() failing when 
parsing xs:dateTime values

xs:dateTime as implemented by Saxon does not pad the 
fractional seconds with zeroes, leading to a parsing error
in ExtensionFunctionsHelper.parseISODate whenever the 
time to be parsed contains a number of milliseconds 
that is divisible by 10. As a consequence, the unit test XFormsExtensionFunctionsTest.testNow() failed in approx.
1 out of 10 executions.

This patch fixes the parsing function and tests the 
modified behavior.