Polish Spring Framework Artifacts table

Issue: SPR-12517
Improve performance of generateKey

Only compute the error message to display when the generated key is
actually null instead of using Assert.notNull as the cache operation
'toString()' method is non trivial and gets computed regardless of the
result.

Issue: SPR-12527
Polish grammar and wording in the reference manual
Improve error handling in CollectionFactory

This commit improves error handling in CollectionFactory by asserting
preconditions.

In addition, this commit introduces ConnectionFactoryTests.
Cover maps & more collections in CollectionFactoryTests
Demonstrate that the CollectionFactory API is not type-safe

This commit introduces test methods in CollectionFactoryTests that
demonstrate how the APIs for createApproximateCollection() and
createApproximateMap() are not type-safe, specifically regarding the use
of generics, raw types, and casting.
Create empty EnumSets & EnumMaps in CollectionFactory

SPR-12483 introduced automatic type conversion support for EnumSet and
EnumMap. However, the corresponding changes in CollectionFactory
contradict the existing contract for the "create approximate" methods
by creating a copy of the supplied set or map, thereby potentially
including elements in the returned collection when the returned
collection should in fact be empty.

This commit addresses this issue by ensuring that the collections
returned by createApproximateCollection() and createApproximateMap()
are always empty.

Furthermore, this commit improves the Javadoc throughout the
CollectionFactory class.

Issue: SPR-12533
Demonstrate that the CollectionFactory API is not type-safe

This commit introduces test methods in CollectionFactoryTests that
demonstrate how the APIs for createCollection() and createMap() are not
type-safe, specifically regarding the use of generics, raw types, and
casting.
Upgrade Jetty to 9.2.6.v20141205
Polish Javadoc regarding default transaction manager
Require non-empty values for TxMgr qualifiers & bean names
Update Eclipse project import script
Fix typo in ide.gradle
Refine EclipseLink SQL logging

Issue: SPR-12528