Replace open4 library by open3

for the following reasons:

1. `open4` is 3rd party library while `open3` is part of StdLib.
2. It is not clear if `popen` is maintained upstream or if it is just
   stable.
3. There needis to be special handling for `IO.popen4` in JRuby while
   `Open3.popen3` should work the same everywhere.

excon.gemspec

@@ -24,7 +24,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency('activesupport')
   s.add_development_dependency('delorean')
   s.add_development_dependency('eventmachine', '>= 1.0.4')
-  s.add_development_dependency('open4')
+  s.add_development_dependency('open3')
   s.add_development_dependency('rake')
   s.add_development_dependency('shindo')
   s.add_development_dependency('sinatra')

lib/excon/test/server.rb

@@ -1,4 +1,4 @@
-require 'open4'
+require 'open3'
 require 'excon'
 require 'excon/test/plugin/server/webrick'
 require 'excon/test/plugin/server/unicorn'
@@ -39,12 +39,9 @@ def initialize(args)
       end
 
       def open_process(*args)
-        if RUBY_PLATFORM == 'java'
-          @pid, @write, @read, @error = IO.popen4(*args)
-        else
-          GC.disable if RUBY_VERSION < '1.9'
-          @pid, @write, @read, @error = Open4.popen4(*args)
-        end
+        GC.disable if RUBY_VERSION < '1.9'
+        @write, @read, @error, wait_thread = Open3.popen3(*args)
+        @pid = wait_thread.pid
         @started_at = Time.now
       end
 

tests/test_helper.rb

@@ -2,7 +2,7 @@
 require 'bundler/setup'
 require 'excon'
 require 'delorean'
-require 'open4'
+require 'open3'
 require 'webrick'
 
 require './spec/helpers/warning_helpers.rb'
@@ -321,12 +321,8 @@ def capture_response_block
 end
 
 def launch_process(*args)
-  unless RUBY_PLATFORM == 'java'
-    GC.disable if RUBY_VERSION < '1.9'
-    pid, w, r, e = Open4.popen4(*args)
-  else
-    pid, w, r, e = IO.popen4(*args)
-  end
+  w, r, e, wait_thread = Open3.popen3(*args)
+  pid = wait_thread.pid
   return pid, w, r, e
 end