Use an int for fractional seconds

[eddelbuettel]

This is a follow-up to #1447 and #1448; it addresses the root cause that the fractional second part should be int as we actually cast explicitly as int and assign NA_INTEGER. The printf format changed in #1448 is reverted back for int too.

The compiler was generally kind to us in the past here and did The Right Thing (TM). The variable is also not used outside the file (unless via an accessor that returns int).

Checklist

• Code compiles correctly
• R CMD check still passes all tests
• Preferably, new tests were added which fail without the change
• Document the changes by file in ChangeLog

[Enchufa2]

LGTM!