Add capability to append to a file, if it already exists, to File Outbound Channel Adapter.
The new attribute is 'append' and is mutually exclusive with 'temporary-file-suffix' since
when appending to a file we can no longer write to a temporary file and then rename it.
INT-2470 addressed PR comments
INT-2470 PR Comments
INT-2470 polishing
changed logic behind File copy when one file needs to be appended into another
INT-2470 added WhileLockedProcessor
INT-2470 polishing
750501d66c