Add support of “with” in @throwable.

It allows to specify the post-state of data.

Example:
    @throwable T1 t1 with this->foo: true;
[auto] Merge from Praspel

    • #824e66a — Add support of “with” in @throwable. (Ivan Enderlin, 2013-06-10)

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Merge remote branch 'library-praspel/master'