Don't always wipe a Model's _schema property when calling setSource()

Only wipe the internal schema cache if listSources() returned a useful
list of sources. Otherwise retain the old schema. This lets datasources
that don't implement listSources to be combined with models that define
static schema properties.

Fixes #2467
Add Configure timezone to boostrap
Fix whitespace error.
Fix whitespace error in Validation utility
Remove smart quotes from Configure timezone in bootstrap
Clean up grammar in Configure timezone in bootstrap
Merge pull request #2494 from bcrowe/hotfix-configTimezone

Add Configure timezone to bootstrap
Fix input type inference when type=>checkbox

FormHelper should not infer types when the explicit type is checkbox.
Instead the provided type should be used.

Fixes #2491
Fix Postgres for bigint primary key.
Correct doc block
Merge pull request #2502 from okinaka/fix-postgres-for-bigint-primary-key

Fix Postgres for bigint primary key.
Merge pull request #2503 from dereuromark/master-string

Correct doc block
Fix incorrectly handled time values around 12:00:00

When using 12 hour formats & intervals, values around 12:00 were
incorrecly converted to midnight.

Fixes #2507
Clarify the docs for DboSource::fetchAll()

Refs #2508
Merge remote-tracking branch 'upstream/master'

Conflicts:
	app/Config/core.php