Eliminate delay in restarting CouchDB when app resumes

* Instead of restarting the entire Erlang VM, just restart the couch_httpd server, which is very fast.
* On wake, check whether the listener socket is still alive, and only restart if it's not.

Change-Id: I00dcd8cf23ca5d9895c07f7f61e698926df1315a
Reviewed-on: http://review.couchbase.org/11017
Tested-by: Farshid Ghods <farshid.ghods@gmail.com>
Reviewed-by: Chris Anderson <jchris@couchbase.com>

Framework/Classes/CouchbaseMobile.m

@@ -192,11 +192,27 @@ - (BOOL)start
     return YES;
 }
 
+- (BOOL)isServerRunning {
+    int port = [_serverURL.port intValue];
+    if (!port)
+        return NO;
+    struct sockaddr_in addr = {sizeof(struct sockaddr_in), AF_INET, htons(port), {0}};
+    int sockfd = socket(AF_INET,SOCK_STREAM, 0);
+    int result = connect(sockfd,(struct sockaddr*) &addr, sizeof(addr));
+    int connect_errno = errno;
+    close(sockfd);
+    if (_logLevel >= 2 && result != 0)
+        NSLog(@"Couchbase: Server not responding (errno=%i)", connect_errno);
+    return result == 0;
+}
+
 - (void) maybeRestart {
-    if (_autoRestart) [self restart];
+    if (_autoRestart && _serverURL && ![self isServerRunning])
+        [self restart];
 }
 
 - (void) restart {
+    _timeStarted = CFAbsoluteTimeGetCurrent();
     [[NSNotificationCenter defaultCenter]
      postNotificationName:kInternalRestartCouchNotification object:nil];
 }