(eldoc-message-commands): Move docstring into comments, since this isn't

(eldoc-message-commands): Move docstring into comments, since this isn't
a user variable.

(eldoc-message-commands-table-size, eldoc-use-idle-timer-p,
eldoc-function-argstring-from-docstring-method-table): Use defvar,
not defconst.

(eldoc-last-data): Use cons explicitly; don't rely on dotted pair read
syntax.  I'm worried the latter might get compiled as read-only data someday.

(eldoc-docstring-message): If truncating symbol name, show ending of name
rather than beginning.  The former is generally more unique.

(eldoc-function-argstring-from-docstring-method-table): Handle
pathological `save-restriction' case.

[top level]: Add `indent-for-tab-command' to eldoc-message-commands.