[eclipselink-dev] Fix for 311899 checked in

[Tom Ware <tom.ware@xxxxxxxxxx>]

https://bugs.eclipse.org/bugs/show_bug.cgi?id=311899

Changes checked in to allow some weaving to work with alternately named and 
located persistence.xml

eclipselink.persistence.xml property must be provided to enable this to work

Limitations:

1. When using with agent-based dynamic weaving this property may only define a 
single location and therefore all persistence units must use that location

2. Java EE servers will still follow the specification (and look for 
META-INF/persistence.xml), so when using an alternate persistence.xml location, 
you will not be able to use injection, and you will not get dynamic weaving

3. You will have to specify the location of the persistence.xml file using the 
-persistencexml argument when using the static weaver (or ther persistencexml 
attribute in the ant tast)