load.c: backtrace of circular require
* load.c (load_lock): print backtrace of circular require via
`Warning.warn` [ruby-core:80850] [Bug #13505]
Send the backtrace of the circular require warning as a single String to Warning.warn
* load.c: send as a single string.
* error.c: expose the string formatted by rb_warning as rb_warning_string().
* test/ruby/test_exception.rb: update tests.
[ruby-core:80850] [Bug #13505]
fix regexp literal warning.
* test/rubygems/test_gem_server.rb: eliminate duplicated character class warning.
[Bug #14481]
merge revision(s) 58471,58493,62436: [Backport #13505]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_2@62441 b2dd03c8-39d4-4d8f-98ff-823fe69b080e