bug#60146: file-exists-in-trash-p needs better name or semantics

[Paul Eggert <eggert@cs.ucla.edu>]

The recently-added function (file-exists-in-trash-p FILE) is poorly 
named since it's not really related to trash - it's simply checking for 
the existence of a directory entry named FILE.

How about extending file-exists-p instead? (file-exists-p FILE t) would 
be like (file-exists-p FILE) except it would not follow symlinks. This 
extension can be implemented via a single system call on POSIX systems, 
and this would be more efficient and would avoid a race in the current 
implementation of file-exists-in-trash-p. (Though of course pretty much 
any use of this new function makes one vulnerable to races....)

If extending file-exists-p is too much, at least please rename 
file-exists-in-trash-p to something like files--exists-nofollow-p, to 
indicate that it's private to files.el and to say better what it means.