* transient_heap.c, transient_heap.h: implement TransientHeap (theap).
  theap is designed for Ruby's object system. theap is like Eden heap
  on generational GC terminology. theap allocation is very fast because
  it only needs to bump up pointer and deallocation is also fast because
  we don't do anything. However we need to evacuate (Copy GC terminology)
  if theap memory is long-lived. Evacuation logic is needed for each type.

  See [Bug #14858] for details.

* array.c: Now, theap for T_ARRAY is supported.

  ary_heap_alloc() tries to allocate memory area from theap. If this trial
  sccesses, this array has theap ptr and RARRAY_TRANSIENT_FLAG is turned on.
  We don't need to free theap ptr.

* ruby.h: RARRAY_CONST_PTR() returns malloc'ed memory area. It menas that
  if ary is allocated at theap, force evacuation to malloc'ed memory.
  It makes programs slow, but very compatible with current code because
  theap memory can be evacuated (theap memory will be recycled).

  If you want to get transient heap ptr, use RARRAY_CONST_PTR_TRANSIENT()
  instead of RARRAY_CONST_PTR(). If you can't understand when evacuation
  will occur, use RARRAY_CONST_PTR().

(re-commit of r65444)


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65449 b2dd03c8-39d4-4d8f-98ff-823fe69b080e