* Add <spel-property-accessors> to configure a list of beans
that implement `org.springframework.expression.PropertyAccessor`
* Add `SpelPropertyAccessorRegistrar` to manage a list of PropertyAccessors
for Integration infrastructure
* Refactoring for `SpelFunctionRegistrar` and `IntegrationEvaluationContextFactoryBean`
to fix the issue when there is no `SpelFunctionRegistrar`(`SpelPropertyAccessorRegistrar`)
in the child AC, but there is one in the parent.
Previously the inheritance did't work for that reason.
* Now parent/child logic moved to `IntegrationEvaluationContextFactoryBean`
* Add documentation
JIRA: https://jira.springsource.org/browse/INT-3133
INT-3133: Rebasing, polishing and documentation
INT-3133: PropertyAccessors override support
* `@Ignore` `SOLingerTests#finReceivedNioLinger()` test
INT-3133: Change JavaDoc link to 3.0.0.RC1
Polishing
- Remove duplicate check - last bean def wins
- Doc Polishing
* add `<spel-function>` XSD element
* add `SpelFunctionParser`
* add `SpelFunctionRegistrar` to avoid introducing some confused 'Method'-bean
* add `SpelFunctionRegistrar` collaboration with `IntegrationEvaluationContextFactoryBean`
* some refactoring for `IntegrationEvaluationContextFactoryBean`
* polishing some failed tests after this change
JIRA: https://jira.springsource.org/browse/INT-1639
INT-1639: SpelFunctionParser use BeanClassLoader
INT-1639: Inherit 'functions' from parent AC
INT-1639: Document the <spel-function>
INT-1639: 'NoSuchBeanDefinitionException' fix
Polishing
