Convert go tree to hierarchical pkg directory:

import (
		"vector" -> "container/vector"
		"ast" -> "go/ast"
		"sha1" -> "hash/sha1"
		etc.
	)

and update Makefiles.  Because I did the conversion
semi-automatically, I sorted all the import blocks
as a post-processing.  Some files have therefore
changed that didn't strictly need to.

Rename local packages to lower case.
The upper/lower distinction doesn't work on OS X
and complicates the "single-package directories
with the same package name as directory name"
heuristic used by gobuild and godoc to create
the correlation between source and binary locations.
Now that we have a plan to avoid globally unique
names, the upper/lower is unnecessary.

The renamings will cause trouble for a few users,
but so will the change in import paths.
This way, the two maintenance fixes are rolled into
one inconvenience.

R=r
OCL=27573
CL=27575

src/lib/os/dir_amd64_linux.go

@@ -5,8 +5,8 @@
 package os
 
 import (
-	"syscall";
 	"os";
+	"syscall";
 	"unsafe";
 )