Hi all,

I came up with two improvements on tab-line-mode:

   1. Suppress-errors...
   It suppresses errors when tab-line-switch-to-prev-tab or
   tab-line-switch-to-next-tab is invoked in the window which has no tabs.
   2. Introduce-a-new-variable... (after #1 patch is applied)
   It introduces a new variable tab-line-switch-cycling which enables
   cycling tab switch.

These patches are attached.
I sent patches for the first time, any advices, comments, or questions are
very welcome.

Best regards,
Katsuyuki