This fixes an error when output is redirected:
```
$ run_ruby -rreline -e '$stderr.puts Reline::Unicode.calculate_width("\u221a").inspect' </dev/null >/dev/null
/home/jeremy/tmp/ruby/lib/reline/ansi.rb:189:in `raw': Operation not supported by device (Errno::ENODEV)
```
The @@encoding -> defined?(@@encoding) changes is necessary because
without that part of the commit, the following error would be raised
by the above command:
```
/home/jeremy/tmp/reline/lib/reline/general_io.rb:10:in `encoding': uninitialized class variable @@encoding in Reline::GeneralIO (NameError)
```
Problem reported and initial patch for Windows provided by
Richard Sharman.
I tested this only on OpenBSD, but hopefully it works for other
operating systems.
Fixes [Bug #17493]
https://github.com/ruby/reline/commit/c001971bb3
IRB uses Reline's 3 dynamic real-time callbacks with calling Ripper;
output_modifier_proc, prompt_proc, and auto_indent_proc. These processing
times make the paste time too long.
https://github.com/ruby/reline/commit/beec3399a8
The command prompt on Windows always uses Unicode to take input and print
output but most Reline implementation depends on Encoding.default_external.
This commit introduces an abstracted structure about the encoding of Reline.
Stan Lo
tomoya ishida
Hiroshi SHIBATA
Samuel Williams
aycabta
Jeremy Evans
Nobuyoshi Nakada