all: single space after period.

The tree's pretty inconsistent about single space vs double space
after a period in documentation. Make it consistently a single space,
per earlier decisions. This means contributors won't be confused by
misleading precedence.

This CL doesn't use go/doc to parse. It only addresses // comments.
It was generated with:

$ perl -i -npe 's,^(\s*// .+[a-z]\.)  +([A-Z]),$1 $2,' $(git grep -l -E '^\s*//(.+\.)  +([A-Z])')
$ go test go/doc -update

Change-Id: Iccdb99c37c797ef1f804a94b22ba5ee4b500c4f7
Reviewed-on: https://go-review.googlesource.com/20022
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Dave Day <djd@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/net/interface_stub.go b/src/net/interface_stub.go
index d1e30f7..f64174c 100644
--- a/src/net/interface_stub.go
+++ b/src/net/interface_stub.go
@@ -7,14 +7,14 @@
 package net
 
 // If the ifindex is zero, interfaceTable returns mappings of all
-// network interfaces.  Otherwise it returns a mapping of a specific
+// network interfaces. Otherwise it returns a mapping of a specific
 // interface.
 func interfaceTable(ifindex int) ([]Interface, error) {
 	return nil, nil
 }
 
 // If the ifi is nil, interfaceAddrTable returns addresses for all
-// network interfaces.  Otherwise it returns addresses for a specific
+// network interfaces. Otherwise it returns addresses for a specific
 // interface.
 func interfaceAddrTable(ifi *Interface) ([]Addr, error) {
 	return nil, nil