Work-around for Eclipse bug regarding EnumSets

This commit introduces superfluous casts in CollectionFactory to
address a bug in Eclipse 4.4.1 that prevents the code from compiling
within Eclipse. Specifically, without these casts Eclipse displays the
following error for use of the EnumSet.copyOf() and EnumSet.noneOf()
methods:

Type mismatch: cannot convert from EnumSet<Enum<Enum<E>>> to
Collection<E>
Suppress "rawtypes" warnings in CollectionFactory

This commit also adds links to the newly created Eclipse bug that was
raised for this issue.
Use public AssumptionViolatedException in Assume

JUnit 4.12 created a 'public' version of the previously 'internal'
AssumptionViolatedException.

This commit upgrades Spring's Assume class to use this new public
version.
Polish reference manual

This commit put more emphasis on Spring Boot in the
"Getting Started" section, and update some outdated excerpts.
List Spring Framework artifacts in the reference manual

Issue: SPR-12517