Replace double [Shift+Alt+L] hack behavior

I've finally found the person behind last week's Shift+Alt+L crazy
behavior, driving me mad :D
I've replaced VsActionManager.LastAction + global var hack with a
another time-based hack :D

It is nearly impossible to solve the double invocation issue completely
(you can't really tell LocateInSolutionExplorer action is the last
action invoked or not), but this hack is a bit better since after 500ms
Shift+Alt+L is guaranteed to behave as usual.

Also I've enabled "activate" flag when showing item in solution explorer
from search (otherwise it's very confusing - something is selected in
solution explorer, but you can't navigate with keyboard).