Initiate the building of a find command.
For example:
(find-cmd '(prune (name ".svn" ".git" ".CVS"))
'(and (or (name "*.pl" "*.pm" "*.t")
(mtime "+1"))
(fstype "nfs" "ufs"))))
`default-directory' is used as the initial search path. The
result is a string that should be ready for the command line.
(fn &rest SUBFINDS)