[merb-helpers] Fix for Merb::Helpers.load_helpers on 1.9.1.
[merb-helpers] Fix for Merb::Helpers.load_helpers on 1.9.1.

Merb::Helpers.load_helpers expect parameter to be an object responding
to each. Which String is not on 1.9.1. So we normalize parameter before
passing it to the method.

merb/merb,wycats/merb,merb/merb,wycats/merb,wycats/merb,wycats/merb,wycats/merb,merb/merb