removal of project's downloads files with same name

Hi, when you upload the two files with same name (i.e. file.zip) to the download section and then delete the one, the other is deleted too (if you tried to download the second one, the missing link error occurs). I think this is because the second file with the same name overwrite the first file.

I think this could be solved with one of these:

1. Disable the upload of the same file name twice
2. Version the each file name appending some counter to the file name after upload