[3.1.0] Continue building up validation functions

- Remove incorrect parsing of value aliases
- Implement most allowed and value alias checks
- Add assertIsBool, assertIsArray and assertIsLookup to ValidatorAtom
- Publish string types in VarParser

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1647 48356398-32a2-884e-a903-53898d9a118a

tests/HTMLPurifier/ConfigSchema/Validator/directive/valueAliasesRealAllowed.vtest

@@ -0,0 +1,11 @@
+ERROR: Alias 'c' in valueAliases in directive 'Ns.Dir' must be an alias to an allowed value
+----
+Ns
+DESCRIPTION: Namespace
+----
+Ns.Dir
+DESCRIPTION: Directive
+TYPE: string
+DEFAULT: 'a'
+ALLOWED: 'a', 'b'
+VALUE-ALIASES: 'c' => 'd'