-different coding style. html_top, html_bottom, internal_link hooks are removed.
-src/move_messages.php code moved to main mailbox listing script. Some hooks are
-broken after implementation of templates in mailbox listing pages. soupNazi()
-function is replaced with checkForJavascript() function. sqimap_messages_delete,
-sqimap_messages_copy, sqimap_messages_flag and sqimap_get_small_header()
-functions are obsoleted. Some IMAP functions return data in different format.
-If plugins depend on changed or removed functions, they will break in this
-SquirrelMail version.
-
-This SquirrelMail version implemented code that unregisters globals in PHP
-register_globals=on setups. If some plugin loads main SquirrelMail functions
-and depends on PHP register_globals, it will be broken.
+different coding style. html_top, html_bottom, internal_link hooks have been
+removed. src/move_messages.php code has been moved to the main mailbox listing
+script. Some hooks may be broken after implementation of templates, especially
+in mailbox listing pages. soupNazi() function has been replaced with the
+checkForJavascript() function. sqimap_messages_delete(),
+sqimap_messages_copy(), sqimap_messages_flag() and sqimap_get_small_header()
+functions are now obsolete. Some IMAP functions return data in different
+format. If plugins depend on changed or removed functions, they will break in
+this version of SquirrelMail.
+
+This SquirrelMail version added http headers that prevent caching of pages by
+proxies. Headers are added in SquirrelMail displayHtmlHeader() function. Changes
+require that html output is not started before displayHtmlHeader() is called. If
+some code starts output, PHP errors will be displayed. If plugins display
+notices in options_save hook and don't stop script execution on error, page
+display will be broken.
+
+SquirrelMail 1.5.1 implemented code that unregisters globals in PHP
+register_globals=on setups. Plugins that load main SquirrelMail functions and
+depend on PHP register_globals=on will be broken.