DWDS/Dialing Concordance Code

+ updated to v2.0.31, including changelog

+ tagged v2.0.31

+ tagged v2.0.30

+ curl LRU-cache fix (all previous queries were getting appended to each new response)

+ avoid bogus 'broken pipe' error messages from subcorpora without hits
- errors arising since get_hit_strings is no longer called for subcorpora without hits

+ set version = 2.0.31-pre1; to be tested on dtaos.beta@...

+ v2.0.31-pre1
- string_socket.cpp: 1 send() per message
- set TCP_NODELAY during create_socket() to disable buffering
- BranchServer: don't send get_hit_strings() if there's nothing to retrieve
+ TODO: stop subcorpora from complaining about this (Error Cannot send string: Broken pipe; errno=32)
- joint work with Adrien Barbaresi

+ added ConcordLib/LRUCache.h : generic template-based LRU cache
- uses STL containers map<> and list<>
- based loosely on discussion from http://stackoverflow.com/questions/2504178/lru-cache-design
- see also gcc-oriented implementation at http://code.google.com/p/lru-cache-cpp/
- idea: use process-local pthread-locked cache for curl responses, avoid sending too many requests
and associated tcp retransmissions which can get SLOW

+ raised chunk-size for socket communications in string_socket.(cpp|h): was=1024; is=4096 (non-win32 only)

+ ddc runtime scripts: renamed ambiguous variables DDC_ROOT(S) to DDC_RUNDIR(S)