remove unnecessary function
Merge branch 'master' into unpin-catalogs
Merge branch 'master' into unpin-catalogs
Merge branch 'master' into unpin-catalogs
Merge branch 'master' into unpin-catalogs
add function to change blocking to non-blocking file descriptor
Provide possibility to register back channels with the cache manager

The back channels work as an opportunistic publish-subscribe mechanism, allowing the cache manager to send information to its clients. Clients can register a pipe with a channel id, an arbitrary string that will be Md5 hashed. The cache manager broadcasts to all registered channels in non-blocking mode.  On errors, the message is lost.  The cache manager will automatically unregister a back channel if the pipe is broken (or on any other error than EAGAIN).

This patch also fixes that broken return pipes kill the cache manager.

This is the foundation for notifications about a high gauge of pinned catalogs.
cosmetics
add stubs for back channels that react to high watermark of pinned catalogs
broadcast high watermark of pinned files
fix file descriptor leak in account map parser
add machinery to start and stop unpin listener
improve logging of pin failures due to full cache
improve high watermark logging
add release of catalogs to the unpin listener
add test case for unpin listener
add cachemgr command to find out protocol revision
ensure that new clients play nicely with old cache managers
Merge branch 'unpin-catalogs'
changelog