failing to load module in psyntax indicates an identifier is not macro

failing to load module in psyntax indicates an identifier is not macro

* module/ice-9/boot-9.scm (false-if-exception): Add optional #:warning
  TEMPLATE ARG... tail, which indicates that we should print a warning
  on failure.
  (load-in-vicinity): Use the new #:warning.
  (make-autoload-interface): Surround the bits that load modules with a
  false-if-exception with #:warning.  Fixes
  http://debbugs.gnu.org/cgi/bugreport.cgi?bug=12202.

* test-suite/tests/syncase.test ("missing autoloads do not foil
  psyntax"): Add a test.