* src/macro.c (expand_macro): In macro expansion errors, report

* src/macro.c (expand_macro): In macro expansion errors, report
line number at open parenthesis.
* src/input.c (next_token): Fix off-by-one bug in reporting end
of file in unterminated comment and string.
(file_names): New obstack, necessary since expand_macro now hangs
on to file names longer than the files remain open.
(input_init): Initialize new obstack.
(push_file): Use new obstack.  Delay updates to current_file
until after expand_macro has restored state.
(peek_input, next_char_1): Update current_file if necessary.
(pop_wrapup): Release memory.
* doc/m4.texinfo (Macro Arguments, Changequote, Changecom): Catch
the off-by-one bug.
(Dnl): Update to the new location reporting rules.
* NEWS: Document these changes.