Hi,
the attached patch makes the parts used by pinentry (and krb5-auth-dialog)
-DSEAL safe so they compile with GTK+ 2.20 with -DSEAL enabled. This is
necessary to keeps things buildable within GNOME 3 (post GTK+ 2.20).
The second patch makes sure pinentry stays buildable with older GTK+ down to 2.12.

I haven't bothered to look at the parts of gtksecentry that would be remove by
#1023.