Prompt for GPG key unlock in systems without pam-gnupg

Resolves #675, #585, #597.

bin/mw

@@ -135,7 +135,7 @@ set ssl_force_tls = yes"
 		pop) synccmd="macro index o \"<shell-escape>mpop $fulladdr<enter>\" \"run mpop to get $fulladdr's mail\""
 			folder="$maildir/$fulladdr"
 			prepmpop ;;
-		*) synccmd="macro index o \"<shell-escape>mw -y $fulladdr<enter>\" \"run mbsync to sync $fulladdr\""
+		*) synccmd="macro index o \"<shell-escape>pass show $fulladdr &> /dev/null; mw -y $fulladdr<enter>\" \"run mbsync to sync $fulladdr\""
 			folder="$maildir/$fulladdr"
 			prepmbsync ;;
 	esac