fix source

[rsteube]

Expands the parsed Source command instead of re-parsing it later.

Works for me so far, but not sure if this is the right approach.

fix #566

[caarlos0]

does this do the same as #551 ?

[rsteube]

Oh, didn't see that one. I think so, but let me see.
Looks like the logged prefix might get lost there though.

This one is a bit tricky, so better have a closer look.