Fix to_timestamp/to_date's handling of consecutive spaces in format string.

When there are consecutive spaces (or other non-format-code characters) in
the format, we should advance over exactly that many characters of input.
The previous coding mistakenly did a "skip whitespace" action between such
characters, possibly allowing more input to be skipped than the user
intended.  We only need to skip whitespace just before an actual field.

This is really a bug fix, but given the minimal number of field complaints
and the risk of breaking applications coded to expect the old behavior,
let's not back-patch it.

Jeevan Chalke