Phobos Unittest

[Per Nordlöw]

When is a phobos unittest supposed to be qualified with version 
`(StdUnittest)`? Ideally, always? I don't see that their current 
use is consistenly following a rule. If so, is the purpose of its 
presence to reduce the burden of the compiler when the 
application using phobos is compiled with -unittest? (edited).

If we were to put a `version (StdUnittest)` in front of every 
`unittest` in phobos (via an automated refactoring of course) 
would that speed building large applications or tests-suites with 
the `-unittest` flag provide they import many/all phobos 
libraries via, for instance, import `std`?

When compiling non-phobos modules with `-unittest` flag, how are 
the `unittest`-blocks in imported phobos modules processed by the 
compiler? Are they only lexed (and parsed) but nothing else?