Fix isSame for differently zoned moments

isSame uses startOf and then compares milliseconds, but this misses the case of
different zones across the moments. startOf('day') in one timezone is different
than the other, so it was never successful.
Use makeAs in calendar too
Use February for isSame tests, so new-year has happened in all timezones
Merge pull request #1371 from ichernev/bugfix/is-same-different-zones

Fix isSame for differently zoned moments