* gc.c (gc_profile_total_time): fix off-by-one error in GC::Profiler.total_time.
* test/ruby/test_gc.rb (class TestGc): test for above.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43457 b2dd03c8-39d4-4d8f-98ff-823fe69b080e