[Dovecot] Patch to fix leak in imap_refresh_proctitle in beta[5, 6]

[Mike Abbott]

The "imap" process of dovecot-2.0.beta[5,6] grows very large (I impose no system limits), e.g. exceeding 4.8GB on a 64-bit system.  These messages appear in the logs:
Warning: Growing pool 'imap client' with: 2048
Warning: Growing pool 'Cache fields' with: 2048
Warning: Growing data stack with: 32768
Warning: Growing data stack with: 65536
Warning: Growing data stack with: 131072
[...]
Warning: Growing data stack with: 1073741824
Warning: Growing data stack with: 2147483648
Warning: Growing data stack with: 4294967296

Every time the data stack grows, the backtrace ends with either:
2   libdovecot.0.dylib                  0x00000001059a35c3 pool_data_stack_realloc + 72 ->
3   libdovecot.0.dylib                  0x0000000105994d59 buffer_alloc + 59 ->
4   libdovecot.0.dylib                  0x0000000105994ef9 buffer_check_limits + 127 ->
5   libdovecot.0.dylib                  0x00000001059950e8 buffer_append + 38 ->
6   imap                                0x0000000105867333 imap_refresh_proctitle + 218 ->
7   imap                                0x000000010585f18e client_command_input + 190 ->
[...]

or

2   libdovecot.0.dylib                  0x00000001059a35c3 pool_data_stack_realloc + 72 ->
3   libdovecot.0.dylib                  0x0000000105994d59 buffer_alloc + 59 ->
4   libdovecot.0.dylib                  0x0000000105994ef9 buffer_check_limits + 127 ->
5   libdovecot.0.dylib                  0x00000001059950e8 buffer_append + 38 ->
6   imap                                0x0000000105867333 imap_refresh_proctitle + 218 ->
7   imap                                0x00000001058666ce cmd_sync_continue + 199 ->
[...]

Here is a patch to fix it:
--- a/src/imap/main.c	(beta6)
+++ b/src/imap/main.c	(working copy)
@@ -39,11 +39,12 @@
 #define IMAP_PROCTITLE_PREFERRED_LEN 80
 	struct client *client;
 	struct client_command_context *cmd;
-	string_t *title = t_str_new(128);
+	string_t *title;
 
 	if (!verbose_proctitle)
 		return;
 
+	title = str_new(default_pool, 128);
 	str_append_c(title, '[');
 	switch (imap_client_count) {
 	case 0:
@@ -72,6 +73,7 @@
 	}
 	str_append_c(title, ']');
 	process_title_set(str_c(title));
+	str_free(&title);
 }
 
 static void client_kill_idle(struct client *client)

And perhaps there should be a warning when data is allocated out of the primordial data stack (as opposed to a nested one)?