Support Groovy scripts in the TCF

Spring Framework 4.0 introduced first-class support for a Groovy-based
DSL for defining the beans for an ApplicationContext. However, prior to
this commit, the Spring TestContext Framework (TCF) did not provide any
out-of-the-box support for using Groovy scripts as path-based resource
locations when loading an application context for tests.

This commit addresses this issue by introducing first-class support for
using Groovy scripts to load the ApplicationContext for integration
tests managed by the TCF. Specifically, the following changes have been
made in the TCF to support Groovy scripts.

 - Introduced getResourceSuffixes() in AbstractContextLoader in order
   to support multiple resource suffixes in the default detection
   process. This feature is used by the new Groovy/Xml context loaders.

 - Introduced GenericGroovyXmlContextLoader and
   GenericGroovyXmlWebContextLoader which support both Groovy scripts
   and XML config files for loading bean definitions. Furthermore,
   these loaders support "-context.xml" and "Context.groovy" as
   resource suffixes when detecting defaults. Note that a default XML
   config file will be detected before a default Groovy script.

 - DelegatingSmartContextLoader and WebDelegatingSmartContextLoader now
   use reflection to choose between using GenericGroovyXmlContextLoader
   and GenericGroovyXmlWebContextLoader vs. GenericXmlContextLoader and
   GenericXmlWebContextLoader as their XML loaders, depending on
   whether Groovy is present in the classpath.

 - Groovy scripts can be configured via the 'locations' or 'value'
   attributes of @ContextConfiguration and can be mixed seamlessly with
   XML config files.

Issue: SPR-11233
Merge from sbrannen/SPR-11233

* SPR-11233:
  Support Groovy scripts in the TCF