compiler: Minor fixes for recover thunks.
compiler: Minor fixes for recover thunks.

Avoid name collisions when a method calls recover.

Don't crash if a method with an unnamed receiver calls
recover.

R=iant
CC=gofrontend-dev
https://golang.org/cl/40520044

qskycolor/gofrontend,anlhord/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,golang/gofrontend,qskycolor/gofrontend,golang/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend