popup: a border, a preedit as wide as its text, one place by the pointer, and no dying

The popup was a white box on the usually white text it covered, with
no edge to tell them apart; it has a border in the separator's colour.
A syllable being composed came in a bar twelve ems wide, wiping out the
line under it: only candidate rows share that steady width now, a
preedit alone hugs its text.  A popup placed by the pointer, when the
client sends no caret, was placed again on every key and so followed
the mouse; it stays where it came up.  Clicks on it no longer fall
through to the root window and its menu.  And one failed draw — a lost
pointer reply, a pixmap the server refused — ended the draw thread and
the popup for the rest of the session; only a dead connection does now.

dat.h

@@ -41,6 +41,7 @@ extern int popupscale;
 #define Fontsz		(32*popupscale)
 #define PopupPad	(4*popupscale)
 #define PopupSep	popupscale
+#define PopupBorder	popupscale
 #define PopupNumw	Fontsz
 #define PopupTextw	(12*Fontsz)
 #define PopupBasew	(2*PopupPad + PopupNumw + PopupTextw)