[RFC] Fix MI timings

[Vladimir Prus <vladimir@codesourcery.com>]

I've noticed that -enable-timings produces broken output for all
commands that resume target. First, we output *stopped.
And them on a separate line we print the timing, like this:

	,time={wallclock="0.32046",user="0.32000",system="0.00000"} (gdb)

This happens because mi_on_normal_stop does print newline, and then
mi_execute_async_cli_command does timings separately. This patch:

1. Make mi_on_normal_stop emit the timing info
2. Stop mi_execute_async_cli_command from doing so
3. Makes captured_mi_execute_command report timing both to MI
and CLI code paths.

I'll commit this in a few days if there are no objections.

- Volodya