poor mv error message

[Eric Blake]

We probably ought to make this error message smarter:

$ mkdir a
$ mv a/. b
mv: cannot move `a/.' to a subdirectory of itself, `b'

Huh?  ./b is not a subdirectory of ./a.  The problem is that rename(2)'s EINVAL 
has two distinct reasons for occuring, either subdirectory recursion (as was 
claimed in the above message), OR when either pathname matches the extended 
regex /(^|\/)\.\.?\/?$/ (as was what really happened).

-- 
Eric Blake