_ci_view_path to _ci_view_paths

[eluser]WanWizard[/eluser]
The underscore indicates a private variable, in PHP4 there was no way to actually make it private.
Now that CI is PHP5, there is. So expect to see more of these changes.

Internal class variables should never be changed directly by 'client' code, but always through a class method where you can control the modification.