cron: add extensions

https://www.man7.org/linux/man-pages/man5/crontab.5.html#EXTENSIONS

src/test/apps-test.js

@@ -337,6 +337,9 @@ describe('Apps', function () {
 
             safe(() => apps._parseCrontab('*/1  *  *  *\t* ')); // no command
             expect(safe.error.message).to.be('Invalid cron configuration at line 1');
+
+            safe(() => apps._parseCrontab('@whatever /bin/false')); // invalid extension
+            expect(safe.error.message).to.be('Unknown extension pattern at line 1');
         });
 
         it('succeeds for crontab', function () {
@@ -353,5 +356,16 @@ describe('Apps', function () {
             expect(result[1].command).to.be('echo "==> This is a custom cron task running every hour"');
 
         });
+
+        it('succeeds for crontab (extensions)', function () {
+            const result = apps._parseCrontab('@reboot /bin/reboot\n\n@weekly /bin/weekly');
+            expect(result.length).to.be(2);
+
+            expect(result[0].schedule).to.be('@reboot');
+            expect(result[0].command).to.be('/bin/reboot');
+
+            expect(result[1].schedule).to.be('0 0 * * 0');
+            expect(result[1].command).to.be('/bin/weekly');
+        });
     });
 });