Improve error handling

* Explain that the error handling is being skipped when GLI_DEBUG is on and error handler returns false
* Do not call the error handler on help requests

Fixes #150
Fixes #151

lib/gli/app_support.rb

@@ -211,6 +211,8 @@ def handle_exception(ex,command)
             commands[:help].execute({},{},command.nil? ? [] : [command.name.to_s])
           end
         end
+      elsif ENV['GLI_DEBUG'] == 'true'
+        stderr.puts "Custom error handler exited false, skipping normal error handling"
       end
 
       raise ex if ENV['GLI_DEBUG'] == 'true'
@@ -254,7 +256,8 @@ def proceed?(parsing_result) #:nodoc:
     # Returns true if we should proceed with GLI's basic error handling.
     # This calls the error block if the user provided one
     def regular_error_handling?(ex) #:nodoc:
-      if @error_block
+      if @error_block 
+        return true if (ex.respond_to?(:exit_code) && ex.exit_code == 0)
         @error_block.call(ex)
       else
         true

test/tc_command.rb

@@ -206,6 +206,48 @@ def test_around_filter_handles_help_now
     assert_contained(@fake_stdout,/SYNOPSIS/)
   end
 
+  def test_error_handler_prints_that_its_skipping_when_gli_debug_is_set
+    ENV["GLI_DEBUG"] = 'true'
+    @app.on_error do
+      false
+    end
+    @app.command :blah do |c|
+      c.action do |*|
+        raise 'wtf'
+      end
+    end
+
+    assert_raises(RuntimeError) {
+      @app.run(['blah'])
+    }
+    assert_contained(@fake_stderr,/Custom error handler exited false, skipping normal error handling/)
+  end
+
+  def test_error_handler_should_be_called_on_help_now
+    @app.command :blah do |c|
+      c.action do |*|
+        help_now!
+      end
+    end
+    @app.run(["blah"])
+    assert @error_called
+  end
+
+  def test_error_handler_shouldnt_be_called_on_help_from_command_line
+    @app.command :blah do |c|
+      c.action do |*|
+      end
+    end
+    [
+      ["--help", "blah"],
+      ["blah", "--help"],
+    ].each do |args|
+      args_copy = args.clone
+      @app.run(args)
+      assert !@error_called, "for args #{args_copy.inspect}"
+    end
+  end
+
   def test_command_skips_pre
     @app.skips_pre
     @app.skips_post