This is Go 1 package renaming CL #4.
This one merely moves the source; the import strings will be
changed after the next weekly release.
This one moves pieces into os, text, and unicode.

exec -> os/exec
scanner -> text/scanner
tabwriter -> text/tabwriter
template -> text/template
template/parse -> text/template/parse
utf16 -> unicode/utf16
utf8 -> unicode/utf8

This should be the last of the source-rearranging CLs.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5331066