skip expiry test for memcache on travis

fixes #877
print travis ENV
travis memcache env check: try again
simplified travis env check for memcache(d)
'yii\mail\MessageInterface' methods 'addText()' and 'addHtml()' removed.
set error_reporting for tests
Email message charset setup added.
Merge branch 'master' of github.com:yiisoft/yii2 into email-swift-2