v0.4.2 - interrupt table.move and plain find under limits

Two more native functions could run past the execution limits and are now interrupted: table.move over a huge range and the plain-text string.find(s, p, 1, true) (quadratic worst case). Behaviour without limits is unchanged.

Known limit: other native functions whose cost depends only on the size of their arguments (sorting a large table with the default comparator, table.concat, string.format...) are not interrupted; bound limits.allocation / limits.totalAllocation to bound the strings they can build.

See CHANGES.md for details.