Sed "@safe pure nothrow"

This simply makes all occurences of the trio "@safe pure nothrow" appear in *that* order. It was already the case 90% of the time, so this only changes the remaining 10%.

Rationale for this change is to help with the ongoing effort to tag with `@nogc`: Having a single grep that can find the trivial functions, so we can easily track down the obvious candidates.

Also, consistency.

@WalterBright : Could you please confirm if this actually helps, and it doesn't create any conflicts on any of your potential current work?