[release-branch.go1.8] all: merge master into release-branch.go1.8

78860b2a cmd/go: don't reject ./... matching top-level file outside GOPATH
2b283ced database/sql: fix race when canceling queries immediately
1cf08182 go/printer: fix format with leading comments in composite literal
b531eb30 runtime: reorder modules so main.main comes first
165cfbc4 database/sql: let tests wait for db pool to come to expected state
ea736493 doc: update gccgo docs
1db16711 doc: clarify what to do with Go 1.4 when installing from source
3717b429 doc: note that plugins are not fully baked
98842cab net/http: don't send body on redirects for 301, 302, 303 when GetBody is set
314180e7 net/http: fix a nit
aad06da2 cmd/link: mark DWARF function symbols as reachable
be9dcfec doc: mention testing.MainStart signature change
a96e117a runtime: amd64, use 4-byte ops for memmove of 4 bytes
4cce27a3 cmd/compile: fix constant propagation through s390x MOVDNE instructions
1be957d7 misc/cgo/test: pass current environment to syscall.Exec
ec654e22 misc/cgo/test: fix test when using GCC 7
256a605f cmd/compile: don't use nilcheck information until the next block
e8d5989e cmd/compile: fix compilebench -alloc
ea7d9e6a runtime: check for nil g and m in msanread

Change-Id: I61d508d4f0efe4b72e7396645c8ad6088d2bfa6e