* src/Makefile.am (EXTRA_DIST): Add icon.
* icons/mail-ext.ico: New, based on breeze message-x-gnu-rmail.svg
* src/inst-kleopatra.nsi: Install and use it.
* src/installer-finish.nsi: Move uninstallation of icon to kleo.
* src/uninst-kleopatra.nsi: Uninstall new and old icon.