Fix various abs() issues.

The abs() function should take an int as argument, but there were
several instances in the code where it was taking an unsigned int or a
double.  In these case, we took one of the following approaches:

* If the argument was a double, use fabs() instead.
* If the argument was unsigned and was certainly going to be positive
  (i.e,. no subtraction), then drop abs() altogether.
* If the argument was unsigned as result of adding or subtracting signed
  and unsigned ints, then we cast all the unsigned ints to signed ints.

WPrefs.app/FontSimple.c

@@ -22,6 +22,7 @@
 #include "WPrefs.h"
 #include <unistd.h>
 #include <fontconfig/fontconfig.h>
+#include <math.h>
 
 /* workaround for older fontconfig, that doesn't define these constants */
 #ifndef FC_WEIGHT_NORMAL
@@ -521,7 +522,7 @@ static void selectedOption(WMWidget * w, void *data)
 				WMListItem *item = WMGetListItem(panel->sizeL, i);
 				int distance;
 
-				distance = abs(size - atoi(item->text));
+				distance = fabs(size - atoi(item->text));
 
 				if (i == 0 || distance < closest) {
 					closest = distance;