curses: don't initialize curses when qemu is daemonized

Current qemu initializes curses even if -daemonize option is
passed. This cause problem because shell prompt appears without
calling endwin().

This patch adds new function, is_daemonized(), to OS dependent
code. With this function, curses_display_init() can check that qemu is
daemonized or not. If daemonized, curses_display_init() isn't called
and the problem is avoided.

Of course, -daemonize && -curses doesn't make sense. Users shouldn't
pass the arguments at the same time. But the problem is very painful
because Ctrl-C cannot be delivered to the terminal.

Cc: Andrzej Zaborowski  <balrog@zabor.org>
Cc: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>
Cc: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Hitoshi Mitake <h.mitake@gmail.com>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>

os-posix.c

@@ -360,3 +360,8 @@ int qemu_create_pidfile(const char *filename)
     /* keep pidfile open & locked forever */
     return 0;
 }
+
+bool is_daemonized(void)
+{
+    return daemonize;
+}

qemu-os-posix.h

@@ -46,4 +46,6 @@ typedef struct timeval qemu_timeval;
 typedef struct timespec qemu_timespec;
 int qemu_utimens(const char *path, const qemu_timespec *times);
 
+bool is_daemonized(void);
+
 #endif

qemu-os-win32.h

@@ -86,4 +86,9 @@ typedef struct {
 } qemu_timeval;
 int qemu_gettimeofday(qemu_timeval *tp);
 
+static inline bool is_daemonized(void)
+{
+    return false;
+}
+
 #endif

vl.c

@@ -3657,7 +3657,9 @@ int main(int argc, char **argv, char **envp)
         break;
 #if defined(CONFIG_CURSES)
     case DT_CURSES:
-        curses_display_init(ds, full_screen);
+        if (!is_daemonized()) {
+            curses_display_init(ds, full_screen);
+        }
         break;
 #endif
 #if defined(CONFIG_SDL)