Small issue on Melange file aspect import

[eduardoafs]

Hi everyone,

I found a small issue, by accident, in the aspect import on .melange file. It is not a big deal but took me some time to find out what was going on, since the stacktrace was not helping.

If you have duplicated imports on the .melange file (i.e. import the same aspect two times) the generation of the adapters will fail. The stacktrace suggests something within the file lock, pointing that a file already exists, the generation is aborted.

Simple bug, simple fix, just check for duplicated entries before running the generator. Trigger a warning might be useful.