Preservation of the executable rights of the files contained in a plugin

[wdlut]

On file systems that support this, the executable rights of a plug-in's files are retained.

[wdlut]

I have not tested it on NTFS or FAT file systems. I don't expect any problems, but it would certainly be good if someone tested it before the merge.

[Ylianst]

I am going to take it and add an if statement to not do this on Windows.