* gc.c (gc_before_sweep): Change algorithm of malloc_limit to
	  conservative for closing to memory consumption of ruby 2.0.

	* gc.c (GC_MALLOC_LIMIT, GC_MALLOC_LIMIT_GROWTH_FACTOR):
	  Adjust parameters for new algorithm.

	Example: make gcbench-rdoc on a pc
                              time       maxrss
	2.0.0p343             285.27     281853952
	trunk before patch    207.19     690405376
	trunk after patch     211.59     312500224


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43558 b2dd03c8-39d4-4d8f-98ff-823fe69b080e