[PATCH] NPE when executing install-plugins and parsed jar has no manifest

The attached Patch fixes two Issues:

1. NPE when executing install-plugins and parsed jar has no manifest:
   In this case an info log message will be generated and the respective jar will be skipped.
2. If you build your Eclipse distribution with maven from scratch - that is all your plugins will be resolved and installed by maven into an assembly directory - it is obstructive to exit the execution of the install-plugins goal when the plugins folder is missing. Thus I changed the code to only output an info message and to create the missing plugin dir.

Hope this helps.

Regards,
Phillip