Weakagree and Alive claims now also allow for a role parameter + BUGFIX.

Previously, weak agreement and aliveness claims would enforce a requirement for all agents in the range
of the rho of the claim run.

For some three-party protocols this was stronger than needed. We now allow an
optional role name parameter for these claims; if such a parameter is used, the claim
is only evaluated for the agents performing that role.

En passant fixed a potential bug: aliveness and weak agreement require a run for each
agent, but previously we didn't check if these were helper protocols. Clearly they
should not be.
Regression-fix: Reintroduced option for alternative PKI.

Changes:

1. Reverted restricted use of 'hashfunction': 'function' can now be used as an alternative (but they are identical).
2. Functions can be specified to be secret, as we had before.

Together with the newer 'inversekeyfunctions' declaration, this allows for the clean definition of alternative key infrastructures.

Example usage:

  secret function sk2;
  function pk2;
  inversekeyfunctions (sk2,pk2);

Conflicts:
	src/compiler.c