time: Renamed PRIscTIME to PRIsdbTIME.

Another remnant of the “syscollector” days ;-)
time: Added sdb_strpunit() to parse a time unit.
frontend/parser: Added support for time interval values.
store, frontend: Parse object field matchers.

Field names are identified as ":<field-name>" and all conditional operators
are supported to compare them against an expression.
frontend/scanner: Simplified handling of reserved words.
t/integration: Execute test scripts using 'set -x'.

A lot of tests fail rather silently. This helps identify the failing test.
frontend: Added 'FILTER' support to the 'LOOKUP' command.

The new syntax is 'LOOKUP <obj> MATCHING <cond> [FILTER <cond>]'.