DWDS/Dialing Concordance Code

+ CheckSatisfiable fix for bibl-constants

* proto docs

+ merged branch ddc-2.2.7+prune -r1530:1548 intro trunk:
* added #PRUNE_ASC[N,KEY(s)] and #PRUNE_DESC[N,KEY(s)] filters
- limit response to at most N hits per count-key given by KEY(s)
- only metadata attributes allowed in KEY(s) (because token-attribute key evaluation needs more ConcSession data populated than we have or want)
* overhauled handling of ':'-operator in both branch and leaf servers
- fixes mantis #50057 ; helps workaround mantis #50058
- actually parse queries in CDDCBranchServer during runq.Init()
- updated query parser (:-operator only allowed *after* all other filters, and *not* in count-query daughters)
- updated server protocol: added optional REQPATH before HINT
+ needed for correct evaluation of ** path-wildcards in ':'-operator subcorpus lists
- added CHost::m_ShortName - without 'server:' prefix
- added CDDCBranchServer::m_HostMap - for less painful daughter-selection
- added CRunQueryData::ReqPath - for tracking request paths (for server VersionCompat >= 2.2.8)
* added new server request nodes - return list of all reachable sub*corpus paths ()

+ bibl2txt.perl: debugging utility

+ ddc 2.2.7: bugfix

+ v2.2.6 release

+ set version = 2.2.6-rc1

- removed hack suppressing initial empty sort-key fields in CDDCBranchServer::GetFirstHitsFromCorpora()
+ hack introduced in v2.1.4 (2017-07-07) as workaround for buggy v2.1.3 empty-field changes
+ appears no longer to be required after disabling COUNT_KEY_COMPAT (i.e. since v2.1.9, 2018-03-08)

+ removed COUNT_KEY_COMPAT macro & related code entirely
- introduced in v2.0.38 (2015-05-20), disabled in v2.1.9 (2018-03-08)

* IndexOneToken(): honor tryFixErrors param for extra columns too