start capturing a session
function () {
			var self = this;
			console.log('starting capture...');
			var req = get_req();
			req.onreadystatechange = function start_capture_response () {
				if (req.readyState === 4) {
					if (req.status == 200) {
						console.log('started.');
						jQuery("#start").hide();
						jQuery("#stop").show();
					  htracr.ui.pulse_logo();
					} else {
						var error = eval("(" + req.responseText + ")");
						alert("Sorry, I can't start the sniffer; it says \"" +
						  error.message + "\"."
						);
						console.log("start problem: " + error);
					}
				}
			};
			req.open("POST", "/start", true);
			req.send("");
			return false;
		}