~/.xinitrc,.xmonad: spawn ssh-agent and forget keys on screen lock.

Inspired by: http://chneukirchen.org/blog/archive/2014/02/the-road-to-openssh-bliss-ed25519-and-the-identitypersist-patch.html

.xinitrc

taffybar&
eval $(ssh-agent -s)
exec xmonad
#exec gnome-session

.xmonad/xmonad.hs

        ((mod4Mask .|. shiftMask, xK_m), spawnHere "quodlibet"),
        ((mod4Mask .|. shiftMask, xK_Tab), spawn "xkbswap"),
        ((mod4Mask .|. shiftMask, xK_l), spawn "slock"),
        ((mod4Mask .|. shiftMask, xK_l), spawn "ssh-add -D && slock"),
        ((0, xK_Print), spawn "scrot -e 'mv $f ~/m/pictures/ 2>/dev/null'"),