[Wien] Fail to open pdf-version within the w2web window.

[Jian-Xin Zhu]

Dear Peter and Respectful Users,

It is a minor.

After w2web session is started, the click on the "pdf-Version" under  
Usersguide in the left panel
just opens another window colored in grey. However, click on "html- 
Version" just works fine.

I notice this problem on Mac Intel systems. Is there a simple fix?

Thanks,

Jianxin