Inactive validators should be considered valid

/cc @rwjblue

If a validator is "inactive" due to its provided `if`
conditional evaling to false, it should be considered
valid rather than preserving its list of errors.
Merge pull request #66 from machty/inactive-validators

Inactive validators should be considered valid
Fix Travis issue with git version.
Merge pull request #67 from rjackson/fix_travis

Fix Travis issue with git version.
Pass property name to conditional validator fn

This allows for conditional validator function reuse
Merge pull request #70 from machty/pass-property-to-conditional

Pass property name to conditional validator fn
Added CHANGELOG
Revalidates arrays when they are replaced.

When an array was replaced the validator was not being updated,
it was just validating the original array.

This problem occurred especially in computed properties
that depend on arrays.
Merge pull request #72 from diogomafra/validate-array

Revalidates arrays when they are replaced.
Refactoring: make 'isValid' a computed property.

The property 'isValid' was being manually updated using observers,
this is not necessary, it's much simpler to just use a computed
property.
Merge pull request #73 from diogomafra/computed-isValid

Refactoring: make 'isValid' a computed property.
Using a computed property macro in the base validator.
Don't emit uncatchable internal promises

Fixes #69
Merge pull request #71 from machty/quiet-promises

Don't emit uncatchable internal promises
Merge pull request #74 from diogomafra/use-macros

Using a computed property macro in the base validator.
Update .travis.yml
add asynchronicity test harness

use a global sequence array to track sequence of event
use a global semaphore to set whether validator should be valid/invalid, so
we can setup tests without triggering the property observers
add a custom assertion 'occursAfter' for asserting on sequence of events
cover the isValid property on the validated model, so we can record when
it is accessed
(failing) test that settling isValid is async and work of validator is async
missing semicolon
rm test 'settling isValid after validate is async'

since isValid is now a computed property, this test is no longer relevant.