Avoid processing columns if there aren't any to allow empty tables.
Fallback to default attribute values when invalid values are used.

When an `ATTRS` setter returns `Y.Attribute.INVALID_VALUE` during
initialization, and a default attribute value is defined, fallback to
that value.

Fixes #2528732
Add more tests for Attribute default value fallback.
Merge branch 'live-docs' of github.com:yui/yui3 into live-docs
fix argument name
Fix #2531914
Create unit test to (dis)prove #2531914.
Merge branch 'dev-master' of github.com:yui/yui3 into dt-2531914
Build Datatable.
Removed erroneous build files.
Merge branch 'attr-init-val' into dev-master

Conflicts:
	src/attribute/HISTORY.md
Build Attribute.
Update "Basic Caching" example to escape user input.
Merge branch 'live-docs' into dev-master
Removed a test that used to fail that no longer does.
build date
Merge branch 'live-docs' of github.com:yui/yui3 into live-docs
Merge branch 'live-docs' into dev-master
Merge branch 'patch-1' of https://github.com/markwoon/yui3 into markwoon-patch-2
Adding unit test for pr #176