Change behavior of GoToFile to not use tabs.

Looks like using tabs is not a good idea as the switchbuf=usetab,newtab
does not honor the newtab when the buffer exists, but is not associated
with any window/tab. So reverting to simply loading the buffer from
current window.

May revisit this decision later ...
New breakpoint commands.

* Created separate commands to get and remove breakpoints.
* These commands take an optional file parameter (% is interpreted as
  current file in which the cursor is located) to restrict the command
  to that specific file.