Properly zero-pad the day-of-year part of the win32 build number

Properly zero-pad the day-of-year part of the win32 build number

This ensure the version number increases over time. The first three digits
in the version number is still set to the actual PostgreSQL version
number, but the last one is intended to be an ever increasing build number,
which previosly failed when it changed between 1, 2 and 3 digits long values.

Noted by Deepak