Files should explicitly include the definitions they directly depend on (#355)

... start by fixing the include files and the fallout in C source from
removing includes not directly needed by headers that previously included
them.

src/common.c

@@ -12,6 +12,7 @@
 #include "version.h"
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <setjmp.h>
 #include <fcntl.h>
 #include <string.h> /* for memset */