Functions to inform user of correct access.

[Nic-Chr]

Initial functions that check and inform the user of their access to the lookups directory.

The way I've set it up is to check access once the package is loaded (either through library or by accessing any function) and if they have access a message appears telling them that this is the case. This message will appear once per session so basically once the package is loaded.
If at the point of loading the package they do not have access, a warning is thrown informing them of this and steps to remedy it.

This is done internally through the check_access() function which throw either an error or a warning, depending on what you prefer (specified through the error_on_no_access arg).

I've done it this way so that when loading the package it doesn't cause a user's entire script to fail just because they may or may not use the lookup files.
But if we want to internally use check_access(), say at the start of get_spd() then an error will be thrown by default if there is no access (unlikely as the access was checked at the point of loading the package).

I've exported a have_access() function which just returns TRUE or FALSE depending on if the user has access to the lookups dir.

[Moohan]

Had another look and all seems good to me.