ambrevar/file: Rename file= to file=? to avoid clash with Serapeum.

Also fix some exports.

.local/share/common-lisp/source/ambrevar/file.lisp

@@ -74,16 +74,16 @@ If none, return the empty string unlike `pathname-type'."
   (or (pathname-type (path file))
       ""))
 
-(export 'directory?)
+(export-always 'directory?)
 (defmethod directory? ((file file))
   (eq (kind file) :directory))
 
-(export 'file?)
+(export-always 'file?)
 (defmethod file? ((file file))
   (eq (kind file) :regular-file))
 
-(export 'file=)
-(defun file= (file1 file2)
+(export-always 'file=?)
+(defun file=? (file1 file2)
   "Return true if FILE1 and FILE2 point to the same file.
 They might not be the same objects."
   (and (file? file1) (file? file2)