r2594 - eval_expression(): $silent arg to hide error messages

r2594  - eval_expression(): $silent arg to hide error messages
 - ibid: return NULL on error and pass returned NULL upwards w/o converting to FALSE
 - getSentencesFromLexems(): rename to getParseTreeFromLexems()
 - getParseTreeFromLexems(): move ACK/NAK decision making to a more general spotPayload()
 - getLexemsFromRackCode(): rename to getLexemsFromRawText()
 - getLexemsFromRawText(): add mock character for better scanner syncing
 - lexError3(): tell scanner state in error message
 - filterEntityList(): moved most of the code into new buildPredicateTable() and new judgeEntity()
 - getIPv4LBList(): new function makes use of the new code to enhance renderVServiceLBForm() and renderRSPoolLBForm()
 - trigger_lvsconfig(): replaced with trigger_isloadbalancer(), which uses IPV4LB_LISTSRC
 - renamed 'LVS config' tab to 'keepalived.conf'