Add local variable with the “let” keyword.

A local variable is a contract variable, it does not represent a data of
the program (class attribute or method argument).

In Praspel:
    @requires let size: 1..5
          and arr: array([…], size);
In PHP
    $requires = $specification->getClause('requires');
    $requires->let['size']->in = realdom()->boundinteger(1, 5);
    $requires['arr']->in       = realdom()->array(…, $requires['size']);
Remove “xor” proposal.
[auto] Merge from Praspel

    • #af13e47 — Add local variable with the “let” keyword. (Ivan Enderlin, 2013-04-09)
    • #eb3820f — Remove “xor” proposal. (Ivan Enderlin, 2013-04-09)

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Merge remote branch 'library-praspel/master'