[dist] README.SETUP: memcached is mandatory now

memcached is not optional anymore it is mandatory for the webUI to work.
[backend] Optimize sourcedeletion function

Optimization done in runtime at revfile rewrite process and do
not fail if a project was deleted during (long) run
[dist] Update README for latest release

+ Clean up a couple of typos and trailing spaces.
[api] Fix ldap incorrect use of 'login' variable
[api] Fix 'user_ldap_strategy.rb' unable to call 'logger.debug' method

make direct call to Rails.logger.debug instead of logger.debug
[backend] transport link chain in remote_getrev if the expansion failed

Should help with stuck 'service in progress' errors.
[api] Fix wrong classname for UserLdapStrategy methods

Commit 8ad64791400f60e03ab336b63ac64b1f79f6fab8
moved ldap related methods out of User class
into a new UserLdapStrategy class and Configuration class
but didn't update the caller in other places
[backend] Move 4 bs_worker config options into BSConfig.pm

1. buildlog_maxsize
2. buildlog_maxidle
3. xenstore_maxsize
4. gettimeout
[backend] make just the buildlog settings configurable
[ci] use repository from 2.5 OBS project
[backend] enable caching of binaries when OBS instance is forwarding it for another instance.
[webui] do not crash when handling remote instance with invalid SSL CA

This happened when adding packman OBS instance and trying to add
a repository in the simple webui view.

Repository targets won't become visible anyway.
[webui] disagreement that this function is not readable anymore :(
[backend] fix forwarding of full tree cpio requests

Only needed for "transitive interconnect" setups, which are currently
not really supported anyway. Still...