Follow Symbol under Cursor should have a timeout

"Follow symbol under cursor" may execute even if the command has been issued a long time ago. If a certain time has passed and/or the user has since navigated elsewhere, or started typing, the command should be dropped.

In a case I just experienced, I wanted to "Follow Symbol under Cursor". When nothing happened after a couple of seconds, I issued it again. When nothing happened after a couple more seconds, I sighed, and manually scrolled up the file, issued a "Find" command which brought me to the desired location within 10-15 s. Then I started typing - and in the middle of that, the "Follow symbol under cursor" became active, and I suddenly typed at a completely different location.