[evolution] Fix broken Help button link for 'Insert > Custom Header' dialog after Mallard transition.

[Andre Klapper <aklapper src gnome org>]

commit 0dc14bba6eb964c6dbf4410da950738c3042c42b
Author: Andre Klapper <ak-47 gmx net>
Date:   Wed Feb 15 12:49:58 2012 +0100

    Fix broken Help button link for 'Insert > Custom Header' dialog after Mallard transition.

 plugins/email-custom-header/email-custom-header.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/plugins/email-custom-header/email-custom-header.c b/plugins/email-custom-header/email-custom-header.c
index ab352d6..4e65f21 100644
--- a/plugins/email-custom-header/email-custom-header.c
+++ b/plugins/email-custom-header/email-custom-header.c
@@ -136,7 +136,7 @@ epech_fill_widgets_with_data (CustomHeaderOptionsDialog *mch)
 	gint set_index_column;
 
 	priv = mch->priv;
-	priv->help_section = g_strdup ("usage-mail");
+	priv->help_section = g_strdup ("mail-composer-custom-header-lines");
 
 	for (set_index_column = 0;
 		set_index_column < priv->email_custom_header_details->len; set_index_column++) {