SafeMapping.has_get():
    Simplify in order to reduce the number of Python bytecodes.  There
    is no longer a branch, which isn't strictly necessary.

Context.evaluateStructure(), .evaluateMacro():
    Since these methods are essentially synonyms for evaluate(), avoid
    the extra method lookup & call by simply making them aliases.

Context.evaluate():
    Re-arrange the try/except/except to avoid some of the exception
    catching by moving part of the try clause into an else clause.