Reduced CPU usage while idle (ref #204, #206).
Improved file/debugger activation on Windows (ref #199).

File activation has been inconsistent, because IsActive() returns `true`,
when it shouldn't, so I changed the logic to request attention first and
then to load file.

Also, this caused a symbol to appear in the loaded file and it turned out
that 307 code we used to enable bringing the window to foreground, was not
correct.