fs-traverse: Add -tails option to remove path prefix

[raimue@…]

fs-traverse currently returns the full path name combined from the path argument and the "local" file name. It would be helpful to have an option to get the "local" part only.

Example:

fs-traverse f /path/to/foo {
    puts $f
}

=>

/path/to/foo/file1
/path/to/foo/file2
...

fs-traverse -strip f /path/to/foo {
    puts $f
}

=>

file1
file2
...

[blb@…]

If we want to be consistent with Tcl, perhaps we should call it -tails like the option for glob?

[raimue@…]

Added in r65785.