1. Table implementations (spec files) can mark the table as 'cachable'.
2. Cached results depend on the shortest/quickest interval of scheduled
queries that act on results of the table.
3. The table API generator blocks caching on index/additional/required
table column options.
This change allows QueryContext constraints to be checked for based on
operator type. This makes checks for the existence of an equality
operator allow enumeration.
Example:
if (context.constraints["pid"].exists(EQUALS)) {
pids = context.constraints["pid"].getAll(EQUALS);
} else {
osquery::procProcesses(pids);
}