Fixes autoloaing errors when PEAR packages are not present
Fixes autoloaing errors when PEAR packages are not present

Before this fix, calls to class_exist will attempt to load the PEAR
classes using autoloaders. Without adding stack_trace() checking (which
is kludgy and slows down standard autoload execution), user defined
classes are indistinguishable from PEAR.

SiftScience/sift-php