merged from libsylph branch.
fixed a bug that automatic account selection was disabled on IMAP4 folders.
save temporary IMAP4 password. Don't try to connect to IMAP4 server when closing folder.
look for all accounts when enable_swap_from is enabled.
enabled custom queue folder.
changed the license of LibSylph from GPL to LGPL.
moved more modules to libsylph.
removed main.h inclusion from account.c.
separated UI code from account.c.
separated UI code from prefs_common.c and prefs_account.c.
added wrappers for C library function that take pathname arguments.
modified several alerts, and added accelerators for the buttons.
modified alert dialogs.
made some buttons stock button.
reimplemented edit account dialog using GtkTreeView.
fixed re-edit crash.
replaced intl.h with glib/gi18n.h.
use GTK stock button for dialog button set.
implemented the migration of configuration.
automatically take over older config files.
Initial import of Sylpheed (GTK2 version).