debugger: show current line, fix for #6150

This patch always shows '>' before current line, see #6150 for reasoning.

If there's a breakpoint, it replaces '*' with '>', so breakpoint on the current line will not be shown anymore. I am in doubt about this.

PS: I'd replace '>' with '→' character because first one makes it harder to read line number. Is there a good way to conditionally insert unicode if it is supported?