fix calloc() calls

* size_t nmemb (number of elements) first, then size_t size
* do not assume char is size 1 but use sizeof()
* allocate for char, not pointer to char (found by Michael McConville,
  fixes #261)

unsupported/UnsupportedProcess.c

@@ -17,7 +17,7 @@ in the source distribution for its full text.
 }*/
 
 Process* UnsupportedProcess_new(Settings* settings) {
-   Process* this = calloc(sizeof(Process), 1);
+   Process* this = calloc(1, sizeof(Process));
    Object_setClass(this, Class(Process));
    Process_init(this, settings);
    return this;