Avoid implicit array to string conversion when logging callback information

A message is logged when callbacks are called.  Unfortunately this log message was interpolating the callback directly into the
logged string -- but callbacks are not always strings.  In PHP 5.4+, this implicit array to string conversion now raises a notice-level error.

http://pear.php.net/bugs/bug.php?id=19704
Make return-by-reference PHP5 compatible.

"Deprecated: Assigning the return value of new by reference is deprecated in/usr/share/pear/Auth.php on line 469"
return directly

per https://github.com/pear/Auth/pull/5/files#r9448442
apply recommendations provided by phpcs --standard=PEAR
Merge pull request #5 from frankfarmer/trunk

Avoid implicit array to string conversion when logging callback information