trayicon.c: fixed trayicon_destroy().
cleanup trayicon on exit.
added 16x16 Sylpheed icon.
some code cleanups.
added mail arrival notification at tray icon.
trayicon.c: fixed compilation failure.
implemented tray icon in Win32.
force iconify even if window is hidden by always-on-top windows when trayicon is clicked.
modified storing into trayicon.
don't enable trayicon action if modal window exists. Present window on click if main window is obscured.
fixed account selector of compose window having unintended mnemonic.
perform show/hide on trayicon click. Implemented popup menu on trayicon.
handle destroy event properly.
enable compilation on MinGW.
separated trayicon into another module, and notify new messages with trayicon on receive.