Make quoting rules less silly

[cpressey]

In a pragma, when you say

...is implemented by shell command "foo"

in "foo", the rules for escaping quotes are awkward. You don't have to backslash-escape double quotes. (Unless of course they are within other double quote inside "foo", but the double-quotes on the outside of "foo" do not count towards the need-to-escape count.)

[cpressey]

This is slightly less silly after #8, i.e. there is now less reason to put quotes inside the shell command. But you still might do that, if you e.g. refer to an unchanging filename (a fixture, perhaps) which has a space in it. Unfortunately I still can't think of a way to change this that makes it significantly less silly.