Update IfHelper.php

To comply with handlebars.js, If adds an extra layer when need to access parents (https://github.com/wycats/handlebars.js/issues/196)
Update UnlessHelper.php

To comply with handlebars.js, If adds an extra layer when need to access parents (https://github.com/wycats/handlebars.js/issues/196)
Add subexpressions with context tests
Update HandlebarsTest.php

Test that check if the if and unless helpers comply with handlebars.js
remove an un-finished test
Merge branch 'patch-6' of github.com:ulriklystbaek/handlebars.php

Conflicts:
	tests/Xamin/HandlebarsTest.php
Merge branch 'patch-3' of github.com:ulriklystbaek/handlebars.php
Merge branch 'patch-4' of github.com:ulriklystbaek/handlebars.php
add extra context layer for if and unless. (Toi match with handlebars.js)
Merge branch 'subexpr_context_test' of github.com:Mibew/handlebars.php
Some changes in tests provided in #80