SI-5923 instantiates targs in deferred macro applications

In January I submitted a pull request, which, as I thought back then,
fixes SI-5923: https://github.com/scala/scala/commit/fe60284769.
The pull request was merged, and everyone was happy that the bug got fixed.

Unfortunately, the fix was: a) incomplete, b) broke something else,
as noticed by Miles in https://groups.google.com/d/topic/scala-internals/7pA9CiiD3u8/discussion.

Now we got a real fix in 2.10.x (https://github.com/scala/scala/commit/90ac5c4e13),
and it's my pleasure to port it to master.