INT-2858: Fix for Repeatable invocation.proceed()

Heretofore there wasn't ability to make some scenario like this, when we want to make failure notification on each retry:

<service-activator>
  <request-handler-advice-chain>
      <bean class="org.springframework.integration.handler.advice.RequestHandlerRetryAdvice"/>
      <bean class="org.springframework.integration.handler.advice.ExpressionEvaluatingRequestHandlerAdvice"
	    p:onFailureExpression="#exception" p:failureChannel-ref="errorOnEachRetryChannel"/>
  </request-handler-advice-chain>
</service-activator>

The second Advice was invoked only once. This was because `ProxyMethodInvocation` keeps the index of current interceptor
on each `invocation.proceed()`, which is recursive by design.

So, change `AbstractRequestHandlerAdvice` to use `((ProxyMethodInvocation) invocation).invocableClone().proceed();`
This way, we get a fresh `MethodInvocation` for the current `Advice` with nested desired advices.

JIRA: https://jira.springsource.org/browse/INT-2858

INT-2858: Polishing; PR Comments

Introduce `AbstractRequestHandlerAdvice.ExecutionCallback#cloneAndExecute()` especially for repeatable Advices, e.g. `RequestHandlerRetryAdvice`
to avoid overhead from `clone()` on simple Advices

INT-2858: Doc ExecutionCallback#cloneAndExecute()

INT-2858 Polishing

Rework docs; add Javadoc; add to test case.
Merge pull request #693 from artembilan/INT-2858
INT-2868 Fix SSL Key Store Resource Handling

Documentation indicates that the keystore and truststore
arguments can be resource patterns (file:..., classpath:..., etc)
but the code always used a ClasspathResource.

Use a PathMatchingResourcePatternResolver to interpret the
pattern correctly.

Add tests.