Log Message:
xa65: update to 2.3.13.

ChangeLog:

  * Fix // and /* */ in quoted strings. Incredible no one ever hit this
    before (thanks ZornsLemma).
  * Segfault fixes for file65, reloc65 and xa. Remember, kids, if you ever
    run xa as root all kittens will die. Please save the kittens (thanks
    Stephen Kitt).
  * Just compare to null in the preprocessor (thanks Bas Wassink).
  * Testsuite expanded.