process: make max number of children (connections) configurable

At least some Panasonic clients try to open more than 5 simultaneous
connections to the server.  If we keep the default of 5 max children,
it results in choppy playback on those clients.

Make this setting configurable, and default to 50 max connections.
Our process is pretty lightweight, so 50 children should not be a
problem on most systems.

process.c

@@ -38,18 +38,20 @@
 #include <signal.h>
 #include <sys/wait.h>
 
+#include "upnpglobalvars.h"
 #include "process.h"
 #include "config.h"
 #include "log.h"
 
-static const int max_number_of_children = 5;
 static int number_of_children = 0;
 
 pid_t
 process_fork(void)
 {
-	if (number_of_children >= max_number_of_children)
+	if (number_of_children >= runtime_vars.max_connections)
 	{
+		DPRINTF(E_WARN, L_GENERAL, "Exceeded max connections [%d], not forking\n",
+			runtime_vars.max_connections);
 		errno = EAGAIN;
 		return -1;
 	}
@@ -63,8 +65,21 @@ process_fork(void)
 void
 process_handle_child_termination(int signal)
 {
-	waitpid(-1, NULL, WNOHANG);
-	--number_of_children;
+	pid_t pid;
+
+	while ((pid = waitpid(-1, NULL, WNOHANG)))
+	{
+		if (pid == -1)
+		{
+			if (errno == EINTR)
+				continue;
+			else
+				break;
+		}
+		else if (pid == 0)
+			break;
+		--number_of_children;
+	}
 }
 
 int