* gc.c: change terminology OLDSPACE -> OLDMALLOC.
  (oldspace -> oldmalloc for variable names)
  OLDSPACE is confusing because it is not includes slots.
  To more clearly, rename such as (oldspace_limit -> oldmalloc_limit).
  It is clear that it measures (estimates) malloc()'ed size.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43833 b2dd03c8-39d4-4d8f-98ff-823fe69b080e