#13 clipboard warnings on copy/paste

[Martin J. Evans]

xfmail 1.5.5 rc1

Whenever text in xfmail is highlighted with the mouse
and copied into a different window I get:

In ClipBoard [clipboard.c 299] Unknown target: 252

in the window(xterm) which started xfmail even though
the text is copied OK. It is a bit annoying as the
xterm which started xfmail is probably doing something
totally different like editing a file.