Doc change: Fix description of certificate matching requirement for app updates.

lifespan of your applications. There are several reasons why you should do so: </p>

<ul>

<li>Application upgrade &ndash; As you release upgrades to your

application, you will want to sign the upgrades with the same certificate, if you

want users to upgrade seamlessly to the new version. When the system is 

installing an update to an application, if any of the certificates in the 

new version match any of the certificates in the old version, then the 

system allows the update. If you sign the version without using a matching

certificate, you will also need to assign a different package name to the 

<li>Application upgrade &ndash; As you release updates to your application, you

will want to continue to sign the updates with the same certificate or set of

certificates, if you want users to upgrade seamlessly to the new version. When

the system is installing an update to an application, it compares the

certificate(s) in the new version with those in the existing version. If the

certificates match exactly, including both the certificate data and order, then

the system allows the update. If you sign the new version without using matching

certificates, you will also need to assign a different package name to the

application — in this case, the user installs the new version as a

completely new application. </li>