Internal now() returns system clock time instead of transaction time

[erimatnor]

In short: ts_get_now_internal uses GetCurrentTime() as its standard time function. This returns system clock instead of the transaction timestamp, which means that the time will vary between each call to this function within the same transaction. Note that the standard now() function returns transaction time, so our internal time function departs from the standard. This can affect queries and other things that rely on getting a consistent time for a transaction.