make sure all programs are 8-byte aligned

* libguile/objcodes.c (OBJCODE_COOKIE): Bump objcode cookie, as we added
  to struct scm_objcode.
* libguile/objcodes.h (struct scm_objcode): Add a uint32 after metalen
  and before base, so that if the structure has 8-byte alignment, base
  will have 8-byte alignment too. (Before, base was 12 bytes from the
  start of the structure, now it's 16 bytes.)

* libguile/vm-engine.h (ASSERT_ALIGNED_PROCEDURE): Add a check that can
  be turned on with VM_ENABLE_PARANOID_ASSERTIONS.
  (CACHE_PROGRAM): Call ASSERT_ALIGNED_PROCEDURE.

* libguile/vm-i-system.c (long-local-ref): Add a missing semicolon.

* libguile/vm.c (really_make_boot_program): Rework to operate directly
  on a malloc'd buffer, so that the program will be 8-byte aligned.

* module/language/assembly.scm (*program-header-len*): Add another 4 for
  the padding.
  (object->assembly): Fix case in which we would return (make-int8 0)
  instead of (make-int8:0). This would throw off compile-assembly.scm's
  use of addr+.

* module/language/assembly/compile-bytecode.scm (write-bytecode): Write
  out the padding int.

* module/language/assembly/decompile-bytecode.scm (decode-load-program):
  And pop off the padding int too.

* module/language/glil/compile-assembly.scm (glil->assembly): Don't pack
  the assembly, assume that assembly.scm has done it for us. If a
  program has a meta, pad out the program so that meta will be aligned.

* test-suite/tests/asm-to-bytecode.test: Adapt to expect programs to
  have the extra 4-byte padding int.

libguile/objcodes.c

@@ -50,7 +50,7 @@
 
 /* The objcode magic header.  */
 #define OBJCODE_COOKIE						\
-  "GOOF-0.7-" OBJCODE_ENDIANNESS "-" OBJCODE_WORD_SIZE "---"
+  "GOOF-0.8-" OBJCODE_ENDIANNESS "-" OBJCODE_WORD_SIZE "---"
 
 /* The length of the header must be a multiple of 8 bytes.  */
 verify (((sizeof (OBJCODE_COOKIE) - 1) & 7) == 0);