* gc.c (add_heap_slots, init_heap): reset heaps_inc zero when
heap slots are expanded by environment variable RUBY_HEAP_MIN_SLOTS.
[ruby-core:39777] [Bug #5380]
* test/ruby/test_gc.rb (test_gc_parameter): add test for it.
* test/ruby/envutil.rb (assert_normal_exit): add :child_env option to
enable pass environemnt variables to child process.
merge revision(s) 33368:
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@33432 b2dd03c8-39d4-4d8f-98ff-823fe69b080e