contains() only supports bytes, not general unicode strings

[FrancescAlted]

This shows the problem:

In [3]: ne.evaluate("contains('abc', 'bc')")
Out[3]: array(True, dtype=bool)

In [4]: ne.evaluate("contains(u'abc', u'bc')")
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-59a7eb2860bb> in <module>()
----> 1 ne.evaluate("contains(u'abc', u'bc')")

/home/faltet/software/numexpr/numexpr/necompiler.pyc in evaluate(ex, local_dict, global_dict, out, order, casting, **kwargs)
    710     expr_key = (ex, tuple(sorted(context.items())))
    711     if expr_key not in _names_cache:
--> 712         _names_cache[expr_key] = getExprNames(ex, context)
    713     names, ex_uses_vml = _names_cache[expr_key]
    714     # Get the arguments based on the names.

/home/faltet/software/numexpr/numexpr/necompiler.pyc in getExprNames(text, context)
    631 
    632 def getExprNames(text, context):
--> 633     ex = stringToExpression(text, {}, context)
    634     ast = expressionToAST(ex)
    635     input_order = getInputOrder(ast, None)

/home/faltet/software/numexpr/numexpr/necompiler.pyc in stringToExpression(s, types, context)
    243         names.update(expressions.functions)
    244         # now build the expression
--> 245         ex = eval(c, names)
    246         if expressions.isConstant(ex):
    247             ex = expressions.ConstantNode(ex, expressions.getKind(ex))

<expr> in <module>()

/home/faltet/software/numexpr/numexpr/expressions.pyc in func(*args)
     86                 args[i] = x = ConstantNode(x)
     87             if not isinstance(x, ExpressionNode):
---> 88                 raise TypeError("unsupported object type: %s" % type(x))
     89         return f(*args)
     90     func.__name__ = f.__name__

TypeError: unsupported object type: <type 'unicode'>

[robbmcleod]

Please redirect any discussion regarding unicode support to #263.