Fix handling zoneinfo files generated by zic 2014c and later.

Fix an error in the conversion of -2**63 from an unsigned integer.

Ignore timestamps that are either far in the past or far in the future
and which currently cause problems for the transition index. This is
primarily intended to ignore the far in the past transition added in zic
2014c (at timestamp -2**63 in zic 2014c and at approximate time of the
big bang from zic 2014d).
Documentation correction.

TZif3 files have been supported for some time.
Move the last -ve transition to the epoch on 32-bit +ve-only platforms.

On platforms that only support positive 32-bit timestamps, move the last
negative 32-bit timestamp to the epoch. This ensures that conversions
are accurate from the epoch onwards instead of just from the first
transition onwards.
Update test data files to version 2014d.

Zoneinfo files were generated with zic version 2014d.
Re-enable the test_time_boundary test on all platforms.

This will now succeed on platforms with 32-bit positive only timestamps.
Prevent YARD from reporting exceptions on abstract methods.

Move the exception raising into a separate method. This prevents YARD
from detecting the exception and reporting it in the documentation.
Since the exceptions will never occur under normal usage, it is
unhelpful for them to appear in the documentation.
Remove unnecessary .new when raising exceptions.
Use seek instead of read to skip the 32-bit section.