Clean the error reporting functions.

Clean the error reporting functions.

* src/report.c: New file.
* src/report.h: Likewise.
* src/Makefile.am: Adjust.
* m4/error.m4: New file.
* m4/Makefile.am: Adjust.
* configure.in (jm_PREREQ_ERROR): Call it.
* src/main.c (int_to_string, banner, fatal_banner, warn_banner):
Remove.
(fatal, fatals): Remove.  All callers use complain.c::fatal.
(warn, warni, warns, warnss, warnss): Remove.  All callers use
complain.c::complain.
(toomany): Remove, use fatal instead.
* src/files.c (done): No argument, use complain_message_count.
* src/main.c (main): Register `done' to `atexit'.

* src/getargs.c (usage): More `fputs', less `fprintf'.