Changing signs of terms like (x-1) after factor or simplification

Hi,

  I use Maxima often to simplify terms or equations that have a lot 
terms of the form (1-x) with variables x in [0,1]. The simplifying 
functions of Maxima tend to transform the terms (1-x) in the less 
intuitive form -(x-1) and I have to convert them back manually. For example,

(%i231) factor(a-x*a);
(%o231) - a (x - 1)

Does anybody know an automatic way to tell Maxima that it shall tranform 
terms like (x-1) into -(1-x) and multiply the minus sign with all other 
minus signs in the product? E.g. I would like

factor(a-x*a);
a (1-x)

or

factor(-a+x*a);
- a (1-x)

Alternatively, is it complicated to write a general function that does 
this transformation? E.g. a function nicesign(expr), yielding:

nicesign(factor(a-x*a));
a (1-x)

Perhaps creating such a function is not too complciated, but I really 
have no knowledge of maxima programming.

Thanks for any help,
Sebastian