Add workaround for lack of A_ITALIC in old ncurses

A_BLINK has probably always existed, but there's no good reason to
ever use it, so make it do italics instead. Normally all attributes
are set by a single set_attributes string if it's set, so clear it
to force ncurses to use the reassigned enter_blink_mode string. If
the terminal has no enter_italics_mode string, then nothing will
happen.

This makes setting multiple attributes a bit less efficient, but I
don't think it's likely to make much of a difference since using
multiple attributes at once is so uncommon.

ui.c

@@ -53,10 +53,6 @@
 #undef lines
 #undef tab
 
-#ifndef A_ITALIC
-#define A_ITALIC A_NORMAL
-#endif
-
 enum {
 	StatusLines = 1,
 	MarkerLines = 1,
@@ -241,6 +237,13 @@ void uiInitEarly(void) {
 	colorInit();
 	atexit(errExit);
 
+#ifndef A_ITALIC
+#define A_ITALIC A_BLINK
+	// Force ncurses to use individual enter_attr_mode strings:
+	set_attributes = NULL;
+	enter_blink_mode = enter_italics_mode;
+#endif
+
 	if (!to_status_line && !strncmp(termname(), "xterm", 5)) {
 		to_status_line = "\33]2;";
 		from_status_line = "\7";