Add vet, lint, and 1.2 builds to travis.
Match error names to btcdb updates.
Changed TxIn.PreviousOutpoint to TxIn.PreviousOutPoint after btcwire API change.
Provide a new median time source API.

This commit provides a new interface, MedianTimeSource, along with a
concrete implementation which allows improved accuracy of time by making
use of the median network time as calculated from multiple time samples.

The time samples are to be provided by callers and are intended to come
from remote clients.

The calculations performed in this implementation exactly mirror those in
Bitcoin Core because time calculations are part of the consensus rules and
hence need to match exactly.
Add 100% test coverage for new median time code.
Modify the time sorter tests to make golint happy.

This commit changes the internal testing mechanism from returning the
unexported timeSorter type directly to insted returning sort.Interface.
This has been done because the latest version of golint complains about
return unexported types.
Update new time tests to prevent false positives.

The new median time tests perform a comparsion of the adjusted time
returned from the median time source to the expected value.  However,
since time is always moving, it is possible the current time between the
call to the adjusted time function and the current time taken in the tests
for comparison just after the call differ by a second due to a boundary
condition.  So, this commit modifies the tests to allow for this
condition.
More false positive prevention in new time tests.

This commit extends the same logic in the previous commit to the
comparison of offsets returned from the median time source in the tests.

In particular it modifies the tests to allow for the offsets to differ by
a second due to a boundary condition to prevent false positives.
Merge remote-tracking branch 'conformal/master' into confmerge

Conflicts:
	.travis.yml
	process.go
	validate.go
	validate_test.go
ppc: merge w/ conformal: tests ok
Merge pull request #5 from mably/confmerge

ppc: merged conformal/master, tests ok