Command::InstallCommand: honor ".gemrc" switches

Fix issue #666 (install-command doesn't seem to honor gemrc)

Also, prettify various messages from "install-command".

lib/pry/commands/install_command.rb

@@ -16,34 +16,31 @@ class Pry
       command = find_command(name)
 
       if command_dependencies_met?(command.options)
-        output.puts "Dependencies for #{command.name} are met. Nothing to do."
+        output.puts "Dependencies for #{ text.green(name) } are met. Nothing to do"
         return
       end
 
-      output.puts "Attempting to install `#{name}` command..."
+      output.puts "Attempting to install #{ text.green(name) } command..."
       gems_to_install = Array(command.options[:requires_gem])
 
       gems_to_install.each do |g|
         next if Rubygem.installed?(g)
-        output.puts "Installing `#{g}` gem..."
-
-        begin
-          Gem::DependencyInstaller.new.install(g)
-        rescue Gem::GemNotFoundException
-          raise CommandError, "Required Gem: `#{g}` not found. Aborting command installation."
-        end
+        output.puts "Installing #{ text.green(g) } gem..."
+        Rubygem.install(g)
       end
 
-      Gem.refresh
       gems_to_install.each do |g|
         begin
           require g
         rescue LoadError
-          raise CommandError, "Required Gem: `#{g}` installed but not found?!. Aborting command installation."
+          fail_msg = "Required gem #{ text.green(g) } installed but not found."
+          fail_msg += " Aborting command installation\n"
+          fail_msg += 'Tips: 1. Check your PATH; 2. Run `bundle update`'
+          raise CommandError, fail_msg
         end
       end
 
-      output.puts "Installation of `#{name}` successful! Type `help #{name}` for information"
+      output.puts "Installation of #{ text.green(name) } successful! Type `help #{name}` for information"
     end
   end
 

lib/pry/rubygem.rb

@@ -57,14 +57,22 @@ class Pry
       # @param [String] name
       # @return [void]
       def install(name)
-        destination = File.writable?(Gem.dir) ? Gem.dir : Gem.user_dir
+        gemrc_opts = Gem.configuration['gem'].split(' ')
+        destination = if gemrc_opts.include?('--user-install')
+                        Gem.user_dir
+                      elsif File.writable?(Gem.dir)
+                        Gem.dir
+                      else
+                        Gem.user_dir
+                      end
         installer = Gem::DependencyInstaller.new(:install_dir => destination)
         installer.install(name)
       rescue Errno::EACCES
         raise CommandError,
-          "Insufficient permissions to install `#{ text.green(name) }`."
+          "Insufficient permissions to install #{ text.green(name) }."
       rescue Gem::GemNotFoundException
-        raise CommandError, "Gem `#{ text.green(name) }` not found."
+        raise CommandError,
+          "Gem #{ text.green(name) } not found. Aborting installation."
       else
         Gem.refresh
       end