Fix 64-bit integer terminal write where high bit set

Using strtoll() can only return numbers in the range [-2^63, 2^63-1]. This
means that 0xffffFFFFffffFFFF (2^64-1) will be out of range and is written as
max LL. Actually, every 64-bit number with high-bit set will wrongly be
written as max LL.

This commit uses strtoull() instead to fix this, and checks for unsiged out-
of-range error. strtoull() also has the neat benefit that input with a minus
sign is treated like C unsigned numbers, ie, -u is also a valid unsigned
number if only u is one. In case the input is meant to be treated as signed,
it is therefore still OK to use strtoull() in the first instance only that in
this case a second check against the range of the signed domain is necessary.

src/term.c

@@ -26,6 +26,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <limits.h>
+#include <errno.h>
 
 #if defined(HAVE_LIBREADLINE)
 #  include <readline/readline.h>
@@ -470,8 +471,9 @@ static int cmd_write(PROGRAMMER * pgm, struct avrpart * p,
       }
 
       // Try integers
-      data.ll = strtoll(argi, &end_ptr, 0);
-      if (*end_ptr || (end_ptr == argi)) {
+      errno = 0;
+      data.ll = strtoull(argi, &end_ptr, 0);
+      if (!(end_ptr == argi || errno)) {
         // Try float
         data.f = strtof(argi, &end_ptr);
         data.is_float = true;