Lint fix: NewApi

Encryptor#init already has a version check, so we can safely wrap the
whole method as @TargetApi(HONEYCOMB)

OAuthWebviewHelper.BaseRinishAuthFlowTask#onPostExecute was using
String.isEmpty, which was added in API 9, but the library project is
currently set to build with API 8. This was replaced with a call to
TextUtils.isEmpty(CharSequence)
Merge pull request #439 from jasonschroeder/Lint-NewApi

Lint fix: NewApi