[rubygems/rubygems] Support the change of did_you_mean about Exception#detailed_message

I am asking did_you_mean to use Exception#detailed_message to add
"Did you mean?" suggestion instead of overriding #message method.

ruby/did_you_mean#177

Unfortunately, the change will affect Gem::UnknownCommandError, which
excepts did_you_mean to override #message method.

This PR absorbs the change of did_you_mean.
Gem::CommandManager now calls #detailed_message method to get a message
string with "Did you mean?" suggestion from an exception.

ruby/rubygems@8f104228d3

Author: mame

lib/rubygems/command_manager.rb

@@ -148,7 +148,12 @@ def command_names
   def run(args, build_args=nil)
     process_args(args, build_args)
   rescue StandardError, Timeout::Error => ex
-    alert_error clean_text("While executing gem ... (#{ex.class})\n    #{ex}")
+    if ex.respond_to?(:detailed_message)
+      msg = ex.detailed_message(highlight: false).sub(/\A(.*?)(?: \(.+?\))/) { $1 }
+    else
+      msg = ex.message
+    end
+    alert_error clean_text("While executing gem ... (#{ex.class})\n    #{msg}")
     ui.backtrace ex
 
     terminate_interaction(1)

test/rubygems/test_gem_command_manager.rb

@@ -80,7 +80,13 @@ def test_find_command_unknown_suggestions
       message << "\nDid you mean?  \"push\""
     end
 
-    assert_equal message, e.message
+    if e.respond_to?(:detailed_message)
+      actual_message = e.detailed_message(highlight: false).sub(/\A(.*?)(?: \(.+?\))/) { $1 }
+    else
+      actual_message = e.message
+    end
+
+    assert_equal message, actual_message
   end
 
   def test_run_interrupt