getting rid of Eclipse JRE_LIB_15

[Andrus Adamchik]

As a reminder, JRE_LIB_15 Eclipse variable is used to work with JDK  
1.5 projects in a JDK 1.4 workspace. It has never been a clean  
solution, but now it causes some serious weirdness when working with  
JPA. Now that migration to Maven saves us from explicit cross-project  
dependencies in Eclipse, I am planning to get rid of it (and just use  
default Eclipse JRE in all projects).

Locally I am going to use two workspaces - one for 1.4 and another -  
for 1.5 projects. But it will be up to a developer how to organize  
his/her Eclipse workspace.

Let me know if this causes problems.

Andrus