INT-3268 Add Simple RemoteFileOperations.get()

Requires a simple `remotePath` arg instead of
a Message<?>.

JIRA: https://jira.springsource.org/browse/INT-3268

Remove extra-class from `this` reference
INT-3266 (S)FTP Close Dirty Cached Sessions

If an exception occurs on a session it should be physically closed
and not reused because its state is indeterminate and the next
operation might fail.

Note: The booleans within CachedSession do not need to be volatile
because it is a short-lived object only used by the current thread.

Also fixes the assertion message in RFT.get().

JIRA: https://jira.springsource.org/browse/INT-3266

INT-3266 Polishing - PR Comments

Remove need for SuppressWarnings.
Fix 2 test cases where the exception has an additional cause.
INT-3266 Java 6 Compiler Compatibility

- ((CachingSessionFactory<?>.CachedSession) session).dirty();
+ ((CachingSessionFactory.CachedSession) session).dirty();

Failed to compile with Java6 (compiles ok with Java7 with
sourceCompatibility=1.6).
INT-3244 Fix RedisMEssageStoreTest Race Condition

JIRA: https://jira.springsource.org/browse/INT-3244
INT-3249: property-placeholder for log-c-a Level

JIRA: https://jira.springsource.org/browse/INT-3249
INT-2688 Add header-type to xpath-header-enricher

JIRA: https://jira.springsource.org/browse/INT-2688
JIRA: https://jira.springsource.org/browse/INT-3237

Doc Polishing.