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/runtime/traceback.go b/src/runtime/traceback.go
index 1d76947..1717624 100644
--- a/src/runtime/traceback.go
+++ b/src/runtime/traceback.go
@@ -115,7 +115,7 @@
 	}
 }
 
-// Generic traceback.  Handles runtime stack prints (pcbuf == nil),
+// Generic traceback. Handles runtime stack prints (pcbuf == nil),
 // the runtime.Callers function (pcbuf != nil), as well as the garbage
 // collector (callback != nil).  A little clunky to merge these, but avoids
 // duplicating the code and all its subtlety.
@@ -706,7 +706,7 @@
 		goroutineheader(gp)
 		// Note: gp.m == g.m occurs when tracebackothers is
 		// called from a signal handler initiated during a
-		// systemstack call.  The original G is still in the
+		// systemstack call. The original G is still in the
 		// running state, and we want to print its stack.
 		if gp.m != g.m && readgstatus(gp)&^_Gscan == _Grunning {
 			print("\tgoroutine running on other thread; stack unavailable\n")