maint: Fix pacman provider to work with Ruby 1.9

Ruby 1.9 doesn't allow the lambda to walk up the directory structure to
require the spec helper This is the same issue as with commit:
f6da3339f59bbd9243a03dc1e417b1fed7955c7e

Also, you can't call each on a string in Ruby 1.9 directly since it
doesn't implicitly do a split on \n like it did in older Rubies, but
each_line works all the way back to 1.8.5

Reviewed-by: Nick Lewis <nick@puppetlabs.com>