Fixes #2612

Old behaviour allowed this, and just deleted the file

mkdir a
mkdir a/b
mv a a/b

New behaviour

mkdir a
mkdir a/b
mv a a/b
mv a a/b
^ cannot move "a" to itself

There was also a second problem related to the first, in other shells, if i try mv with more than one source, it just ignores the destination file. So that one file will not break the whole process. I decided to add this behavior. It now works like this.

mkdir foo bar fizz
mv * fizz
ls fizz
foo bar

I have two questions now
1 - Should i give some type of warning that some files will not be moved(just like the classic mv command), and if so how could i give this warning without stopping the process?
2 - I decided to make the "sources" variable mutable and use a filter to remove the error files, i could also do this checking in the for loop that moves the files(Line 501), but i thought this way would make the code less readable given that there would be a piece of code that does two different things at the same time. Was that the best decision?