Avoid shadowing variables in some Eshell command forms
* lisp/eshell/esh-cmd.el (eshell-rewrite-for-command): Make
'for-items' an uninterned symbol.
(eshell-as-subcommand): Correct docstring.
(eshell-do-command-to-value): Mark obsolete.
(eshell-command-to-value): Move binding of 'value' outside of the
macro's result, and remove call to 'eshell-do-command-to-value'.