doc: go1.6.txt: go doc searches in breadth-first order

Change-Id: I12a43b15e81a5e0b174c1c49e77f8307c567233b
Reviewed-on: https://go-review.googlesource.com/17697Reviewed-by: Rob Pike <r@golang.org>

doc/go1.6.txt

 Tools:
 
 cmd/dist: use clang on FreeBSD (https://golang.org/cl/16635)
+cmd/doc: search packages in breadth-first order (https://golang.org/cl/17691)
 cmd/go: vendoring enabled by default (https://golang.org/cl/13967/)
 cmd/go: flags for tests must precede package name if present; also makes it easier to pass flags to test binaries (https://golang.org/cl/14826)
 cmd/go: add -msan option (https://golang.org/cl/16169)