make rebuild-ccl print path to sources

[xrme]

Sometimes it happens that CCL_DEFAULT_DIRECTORY ends up being set in the environment, and points to sources in an unexpected location.

This can cause weird errors (e.g., "Error: The value 0 is not of the expected type STRUCTURE") when evaluating rebuild-ccl. Much confusion and frustration can result (like in #211, for example).

We should print out the truename of the ccl: logical host when doing rebuild-ccl so that people have a chance of noticing this situation.