[tz] Proposed patch - Theory notes for backward file

[Paul Eggert]

Zefram wrote:
> For the "backward" file to be removable
> what you need is that the "backward" file does not contain any "active"
> entries.  No other files containing "inactive" entries is what's needed
> to have an easy way of feeding only "active" entries to zic.  Maybe you
> want both of these things?

I think Stephen wants both: he wants canonicalization, and he
wants 'backward' to be removable.  But 'backward' really has
only the second role; it doesn't have the first one.

It's reasonable to note the second role in 'Theory'.
I've pushed the following proposed patch to do that;
it says essentially what Stephen proposed, albeit more briefly.
Canonicalization we can leave for another day.

* Theory: Say that excluding 'backward' should not affect other data.
Suggested by Stephen Colebourne in
<http://mm.icann.org/pipermail/tz/2013-September/019939.html>.
diff --git a/Theory b/Theory
index 39ef7ac..13b5565 100644
--- a/Theory
+++ b/Theory
@@ -368,7 +368,8 @@ this relationship is not exact and is not true for 'time.tab'.
 Older versions of this package used a different naming scheme,
 and these older names are still supported.
 See the file 'backward' for most of these older names
-(e.g. 'US/Eastern' instead of 'America/New_York').
+(e.g. 'US/Eastern' instead of 'America/New_York');
+excluding 'backward' should not affect the other data.
 The other old-fashioned names still supported are
 'WET', 'CET', 'MET', and 'EET' (see the file 'europe').