make optional providers optional to osgi

Only Major because it's easy to fix

Generated osgi metadata in the dist jars do not have packages optional for providers that ARE optional.

If you look in providers.xml you can see some providers shouldn't load based on where classes are present. However the osgi manifest requires these classes (currently). To make these classes also optional to osgi you need to change commons-vfs2-project pom.xml to include the property:

<properties>
<!-- existing properties, then... -->
<commons.osgi.import>com.jcraft.jsch.*;resolution:=optional,
javax.crypto.*;resolution:=optional,
org.apache.commons.httpclient.*;resolution:=optional,
org.apache.commons.net.ftp.*;resolution:=optional,
org.apache.jackrabbit.webdav.*;resolution:=optional,
*</commons.osgi.import>
</properties>