easy way of writing not implemented macros

Even though it's easy to mark regular method bodies as stubs (using ???),
there's no simple way of doing the same for macro methods. This patch
fixes the inconvenience.
SI-5886 Remove check for packed type conformance.

Nothing breaks. Why did by-name arguments have this
extra check? What's the difference to a () => T?

The check was added originally in 8414eba.
Merge pull request #2537 from adriaanm/ticket-5886

SI-5886 Remove check for packed type conformance.
Fix for unreachable code warning.

Oops, I miss when unreachable code was an error.
Merge pull request #2547 from paulp/issue/bogus-warning

Fix for unreachable code warning.
Merge pull request #2497 from scalamacros/topic/macro-qqq

easy way of writing not implemented macros
SI-7464 allows FieldMirror.set to update vals

There's no reason to leave such sentinels in place inside a facility
designed to circumvent usual restrictions of static types / visibility.
Merge pull request #2504 from scalamacros/ticket/7464

SI-7464 allows FieldMirror.set to update vals
Reimplementing blocking awaiting for Futures so only the blockers have to pay for it.