Solaris needs inclusion of signal.h for signal()

Currently the compilation fails in connect.c and merge-index.c

Signed-off-by: Junio C Hamano <junkio@cox.net>

connect.c

@@ -8,6 +8,7 @@
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <netdb.h>
+#include <signal.h>
 
 static char *server_capabilities = NULL;
 

merge-index.c

@@ -1,5 +1,6 @@
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <signal.h>
 
 #include "cache.h"