Add Linux pager support for cartridges list and help

lib/rhc/command_runner.rb

@@ -137,6 +137,7 @@ def run_help(args=[], options=nil)
         say "See '#{program :name} help' for a list of valid commands."
         1
       else
+        RHC::Helpers.pager
         command = command(cmd)
         help_bindings = CommandHelpBindings.new command, commands, self
         say help_formatter.render_command help_bindings

lib/rhc/commands/cartridge.rb

@@ -35,6 +35,8 @@ class Cartridge < Base
     def list
       carts = rest_client.cartridges.sort_by{ |c| "#{c.type == 'standalone' && 1}_#{c.tags.include?('experimental') ? 1 : 0}_#{(c.display_name || c.name).downcase}" }
 
+      pager
+
       if options.verbose
         carts.each do |c|
           paragraph do 

lib/rhc/helpers.rb

@@ -229,7 +229,7 @@ def color(*args)
       $terminal.color(*args)
     end
 
-    [:indent, :paragraph, :section, :header, :table, :table_args].each do |sym|
+    [:pager, :indent, :paragraph, :section, :header, :table, :table_args].each do |sym|
       define_method(sym) do |*args, &block|
         $terminal.send(sym, *args, &block)
       end

lib/rhc/highline_extensions.rb

@@ -162,6 +162,34 @@ def paragraph(&block)
     section(:top => 1, :bottom => 1, &block)
   end
 
+  def pager
+    #:nocov:
+    return if RUBY_PLATFORM =~ /win32/
+    return unless @output.tty?
+
+    read, write = IO.pipe
+
+    unless Kernel.fork # Child process
+      STDOUT.reopen(write)
+      STDERR.reopen(write) if STDERR.tty?
+      read.close
+      write.close
+      return
+    end
+
+    # Parent process, become pager
+    STDIN.reopen(read)
+    read.close
+    write.close
+
+    ENV['LESS'] = 'FSRX' # Don't page if the input is short enough
+
+    Kernel.select [STDIN] # Wait until we have input before we start the pager
+    pager = ENV['PAGER'] || 'less'
+    exec pager rescue exec "/bin/sh", "-c", pager
+    #:nocov:
+  end
+
   private
     def separate_blocks
       if (@margin ||= 0) > 0 && !@last_line_open