Assorted `syntax-check' fixes.

Assorted `syntax-check' fixes.

* doc/ref/Makefile.am ($(snarf_doc).am): Untabify.

* libguile/eval.c: Remove unnecessary <assert.h> inclusion.

* .x-sc_m4_quote_check: Update.

* libguile/error.c (scm_error_scm): Use `EXIT_FAILURE' instead of 1.
* libguile/init.c (fixconfig, scm_boot_guile): Likewise.
* libguile/null-threads.h (scm_i_pthread_exit): Likewise.
* libguile/script.c (scm_compile_shell_switches): Likewise.
* test-suite/standalone/test-conversion.c: Likewise.
* test-suite/standalone/test-list.c: Likewise.
* test-suite/standalone/test-unwind.c: Likewise.

* libguile/async.c: Remove unnecessary inclusion of <signal.h>.

* NEWS: "filesystem" -> "file system".
* doc/ref/r6rs.texi: Ditto.

* cfg.mk (local-checks-to-skip): New variable.

* .x-sc_m4_quote_check, .x-sc_obsolete_symbols, .x-sc_program_name,
  .x-sc_prohibit_atoi_atof, .x-sc_prohibit_magic_number_exit: New
  files.

* .gitignore: Update.