Add callables.c to EXTRA_DIST=

Originally committed to SVN as r1941.

auto3/Makefile.am

 if HAVE_AUTO3_LUA
-lib_LTLIBRARIES = libaegisub-auto3.la
+
 AM_CFLAGS = -DAUTO3LIB @LUA50_CPPFLAGS@
 AM_LDFLAGS = @LUA50_LDFLAGS@
+
+lib_LTLIBRARIES = libaegisub-auto3.la
 libaegisub_auto3_la_SOURCES = auto3.c
 noinst_HEADERS = auto3.h
+
 endif
+
+EXTRA_DIST= callables.c