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/unix/modsocket.c b/unix/modsocket.c
index 5f3fdaa..6bdbc88 100644
--- a/unix/modsocket.c
+++ b/unix/modsocket.c
@@ -32,7 +32,7 @@
 // Helper functions
 #define RAISE_ERRNO(err_flag, error_val) \
     { if (err_flag == -1) \
-        { nlr_jump(mp_obj_new_exception_msg_varg(&mp_type_OSError, "[Errno %d]", error_val)); } }
+        { nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_OSError, "[Errno %d]", error_val)); } }
 
 STATIC void get_buffer(mp_obj_t obj, buffer_info_t *bufinfo) {
     mp_obj_base_t *o = (mp_obj_base_t *)obj;
@@ -46,7 +46,7 @@
     return;
 
 error:
-    nlr_jump(mp_obj_new_exception_msg(&mp_type_TypeError, "Operation not supported"));
+    nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "Operation not supported"));
 }
 
 STATIC mp_obj_socket_t *socket_new(int fd) {
@@ -264,7 +264,7 @@
     const char *s = mp_obj_str_get_str(arg);
     struct in_addr addr;
     if (!inet_aton(s, &addr)) {
-        nlr_jump(mp_obj_new_exception_msg(&mp_type_OSError, "Invalid IP address"));
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Invalid IP address"));
     }
 
     return mp_obj_new_int(addr.s_addr);
@@ -277,7 +277,7 @@
     const char *s = mp_obj_str_get_str(arg);
     struct hostent *h = gethostbyname(s);
     if (h == NULL) {
-        nlr_jump(mp_obj_new_exception_msg_varg(&mp_type_OSError, "[Errno %d]", errno));
+        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_OSError, "[Errno %d]", errno));
     }
     assert(h->h_length == 4);
     return mp_obj_new_int(*(int*)*h->h_addr_list);
@@ -309,7 +309,7 @@
     int res = getaddrinfo(host, serv, NULL/*&hints*/, &addr);
 
     if (res != 0) {
-        nlr_jump(mp_obj_new_exception_msg_varg(&mp_type_OSError, "[addrinfo error %d]", res));
+        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_OSError, "[addrinfo error %d]", res));
     }
     assert(addr);