(gdb-var-create-handler): Move speedbar

(gdb-var-create-handler): Move speedbar
call to...
(gud-watch): ...here so speedbar is raised for already watched
expressions.
(gdb-speedbar-refresh): Delete function.
(gdb-speedbar-update, gdb-speedbar-timer-fn): New functions.
Use speedbar-timer-fn instead of speedbar-refresh (reverting
earlier change).
(gdb-var-evaluate-expression-handler)
(gdb-var-list-children-handler-1, gdb-var-update-handler-1):
Use it.