incorrect value for 'last' in validatio rules

As said in documentation:
"If set to true and the current rule does not validate, the current validation error message is then returned and all following rules for the current field will not be checked."
Merge pull request #3879 from mohsen-ekhtiari/patch-1

incorrect value for 'last' in validatio rules
Backport changes from cakephp/cakephp#3959 to 1.3

Backport race condition fixes from 2.x to 1.3. This is a severe enough
issue that it warrants a fix.

Refs #3857
Fix failing tests.

These tests were failing as integers were not being quoted as strings
which is expected for me at least.
Bump version to 1.3.20