[Webtest] additional xdoclet merge points

[Paul King]

Note for developers:

I have added two additional merge points for xdoclet. If you write
(currently an extension) called for example MyCustomStep.java, xdoclet
generation will proceed as follows:

1. Generate class level info, i.e. @webtest.step info (as before)

2. Include/merge MyCustomStep-syntax-pre.xml

3. Iterate over all method level info, i.e. @webtest.parameter info (as before)

4. Include/merge MyCustomStep-syntax-post.xml

The syntax xml files use the standard "whitePaper" style and
need to be placed in a subdirectory corresponding to the
Java package of MyCustomStep.java.

Have a look at ScriptStep for an example.

Paul.