Add -q/--quieter flag to suppress notes about class/function

[gvanrossum]

Fixes #1821 (well enough for me to close it).

[gvanrossum]

I made this an option so that we can experiment with it.

My main reason for wanting it now is that I have a rather large test with a bunch of errors aimed at specific lines, and I really want to use the # E: ... notation. The test (by its nature) contains several functions, so there would be several "In function ..." notes interspersed with the interesting errors (and the # E notation doesn't support that). Using this diff I can add "quieter" to the # options: section of the test to suppress those notes, so using # E becomes possible.

By leaving the default unchanged I won't have to clean up the zillions of other tests expecting these notes.

[ddfisher]

I worry that this PR will lead to us never fixing the user-facing aspects of #1821. I'd much rather see us do that all in one fell swoop.

Don't we have a flag for automatically fixing up test files?

[ddfisher]

Aside from that, it would be nice for this to have a more specific name.

[ddfisher]

I missed that this PR added a user-facing flag. With that in mind, this seems like a reasonable first step.