Ruby

time.c (time_strftime): avoid garbage in common case

strftime format strings which are dynamically-generated will benefit
from avoiding garbage, here.

• time.c (time_strftime): use rb_str_tmp_frozen_{acquire,release}
• test/ruby/test_time.rb (test_strftime_no_hidden_garbage): new test

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57476 b2dd03c8-39d4-4d8f-98ff-823fe69b080e