sh changes

[Andrew Koenig]

> In case you missed it, the difference is the extra colon in the Sun 3.0
> system. Questions: when and why was this change made?  Are there any
> other variants of Unix with this change? Has anybody's command file
> broken on account of this?

In case you missed it, the other difference is "if parameter is set"
vs. "if parameter is set and non-null."  I believe that the Sys V
shell supports both usages.  The point is that a parameter that
is not set is not necessarily the same as one that is set to null.