Fix integer overflow issue in ZoneInfo.

The least messy fix is to change mTransitions to long[] despite
the underlying tzdata being ints. This leads to neater code than
comparing the unix time (as a long) against the first and last
element of the transitions array.

bug: 18839557

Change-Id: Ife562749e8b2160f664d566a0a2aae14a0aea36e
Merge "Fix integer overflow issue in ZoneInfo."