* gc.c: introduce new environment variable
  "RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR" to control major/minor GC
  frequency.
  Do full GC when the number of old objects is more than R * N
  where R is this factor and
                N is the number of old objects just after last full GC.
* test/ruby/test_gc.rb: add a test.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45021 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Conflicts:
	ChangeLog
	gc.c