py: Change nlr_jump to nlr_raise, to aid in debugging.

This does not affect code size or performance when debugging turned off.

To address issue #420.
diff --git a/py/objint.c b/py/objint.c
index 1ea6a4f..a1d3924 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -49,7 +49,7 @@
         }
 
         default:
-            nlr_jump(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "int takes at most 2 arguments, %d given", n_args));
+            nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "int takes at most 2 arguments, %d given", n_args));
     }
 }
 
@@ -73,13 +73,13 @@
 
 // This is called only with strings whose value doesn't fit in SMALL_INT
 mp_obj_t mp_obj_new_int_from_long_str(const char *s) {
-    nlr_jump(mp_obj_new_exception_msg(&mp_type_OverflowError, "long int not supported in this build"));
+    nlr_raise(mp_obj_new_exception_msg(&mp_type_OverflowError, "long int not supported in this build"));
     return mp_const_none;
 }
 
 // This is called when an integer larger than a SMALL_INT is needed (although val might still fit in a SMALL_INT)
 mp_obj_t mp_obj_new_int_from_ll(long long val) {
-    nlr_jump(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
+    nlr_raise(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
     return mp_const_none;
 }
 
@@ -89,7 +89,7 @@
     if ((value & (WORD_MSBIT_HIGH | (WORD_MSBIT_HIGH >> 1))) == 0) {
         return MP_OBJ_NEW_SMALL_INT(value);
     }
-    nlr_jump(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
+    nlr_raise(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
     return mp_const_none;
 }
 
@@ -97,7 +97,7 @@
     if (MP_OBJ_FITS_SMALL_INT(value)) {
         return MP_OBJ_NEW_SMALL_INT(value);
     }
-    nlr_jump(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
+    nlr_raise(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
     return mp_const_none;
 }