double-quoted UTF8 hash key has the wrong encoding #2591
Description
The following test.rb works on MRI Ruby 2.2.0,
but gives the wrong encoding and ArgumentError on master.
test.rb
# encoding: utf-8
h = { "Ãa1": true }
puts h.keys.first.encoding
puts h
MRI Ruby 2.2.0
$ ruby ~/development/test.rb
UTF-8
{:Ãa1=>true}
JRuby master
$ jruby ~/development/test.rb
US-ASCII
ArgumentError: invalid byte sequence in US-ASCII
inspect at org/jruby/RubySymbol.java:241
inspect at org/jruby/RubySymbol.java:230
inspect at org/jruby/RubyHash.java:844
to_s at org/jruby/RubyHash.java:909
puts at org/jruby/RubyIO.java:2406
puts at org/jruby/RubyKernel.java:542
__script__ at /Users/k77ch7/test.rb:4
My env
jruby 9.0.0.0-SNAPSHOT (2.2.0p0) 2015-02-12 1c1838e Java HotSpot(TM) 64-Bit Server VM 25.5-b02 on 1.8.0_05-b13 +jit [darwin-x86_64]