JAF should find META-INF/mailcap files everywhere in CLASSPATH on JDK 1.2

The javax.activation.MailcapCommandMap class only
looks at the first META-INF/mailcap file in the
CLASSPATH, instead of merging the content of all
of them.

This seriously degrades the ability to ship a set
of classes and their corresponding mailcap file,
and expect it to reliably work in an end-user's
environment. For eaxample, if the javamail mail.jar
file is in the standard extensions dircectory
of a JDK1.2 installation, the mailcap file from
there is selected in preference to the one shipped
with a set of classes to handle a specific function
or datatype.

(Review ID: 38760)