Removes "double paren" issue for boolean / if function

[matthew-dean]

See tests, allows more intuitive form for simple conditions:

  @f: boolean(3 = 4);
  f: if(not(@f), 6);
  g: if(true, 3, 5);
  h: if(false, 3, 5);

Note: multiple conditions still require parens around conditions without refactoring e.g.

if ((true) and (true), 3, 5);

EDIT: this is now fixed. You can write:

if (true and true, 3, 5);

[matthew-dean]

This is low risk and pointed out at the time of implementation as a flaw, so I'll just merge.