Transposing an expression not supported and leads to strange error

[jonnyhyman]

In trying to transpose an atoms.smul instance, I ran into a strange error during the deepcopy phase.

File "c:\users\__jonny__\dropbox\compute\convexoptimization\convex_symbolic\cvx_sym\symbolic.py", line 354, in T
    transpose = copy.deepcopy(self)
  File "C:\Python36-64\lib\copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "C:\Python36-64\lib\copy.py", line 280, in _reconstruct
    state = deepcopy(state, memo)
  File "C:\Python36-64\lib\copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "C:\Python36-64\lib\copy.py", line 240, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "C:\Python36-64\lib\copy.py", line 150, in deepcopy
    y = copier(x, memo)
  File "C:\Python36-64\lib\copy.py", line 215, in _deepcopy_list
    append(deepcopy(a, memo))
  File "C:\Python36-64\lib\copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "C:\Python36-64\lib\copy.py", line 274, in _reconstruct
    y = func(*args)
  File "C:\Python36-64\lib\copyreg.py", line 88, in __newobj__
    return cls.__new__(cls, *args)
  File "c:\users\__jonny__\dropbox\compute\convexoptimization\convex_symbolic\cvx_sym\operations\atoms\muls.py", line 39, in __new__
    return sym.Constant(args[0].value * args[1].value)
IndexError: tuple index out of range

It appears in doing the deepcopy, the new method was called on the smul and misinterpreted the args as constants.

For now, transpose only symbols directly. In the future, will need to implement a transpose method for functions.