cmd/cover: syntax error near GoCover_0

[dvyukov]

Source code is:

$ cat pkg/pkg.go

package pkg
func foo() {
    switch i := (interface{})(nil); i.(type) {
    }
}

$ cat pkg/pkg_test.go

package pkg

Compilation fails with the following error message:

$ go test -c -cover pkg
# pkg
/var/folders/00/0zkq0000h01000cxqpysvccm003y_w/T/go-build695841649/pkg/_test/_obj_test/pkg.go:6: syntax error near GoCover_0
/var/folders/00/0zkq0000h01000cxqpysvccm003y_w/T/go-build695841649/pkg/_test/_obj_test/pkg.go:8: syntax error near 1

[dvyukov]

@alandonovan