Expose trap once-field to lua

doc/lua.adoc

@@ -201,6 +201,7 @@ Returns a table with the following elements:
 | ttyp_name   | text    | name of trap type
 | tseen       | boolean | trap seen by you?
 | madeby_u    | boolean | trap made by you?
+| once        | boolean | trap is deleted once triggered
 | tnote       | integer | note of a squeaky board trap
 | launchx, launchy, launch2x, launch2y | integer | coordinates of a boulder for a rolling boulder trap
 | conjoined   | integer | encoded directions for a [spiked] pit.

src/nhlua.c

@@ -432,6 +432,7 @@ nhl_gettrap(lua_State *L)
                                     get_trapname_bytype(ttmp->ttyp));
             nhl_add_table_entry_bool(L, "tseen", ttmp->tseen);
             nhl_add_table_entry_bool(L, "madeby_u", ttmp->madeby_u);
+            nhl_add_table_entry_bool(L, "once", ttmp->once);
             switch (ttmp->ttyp) {
             case SQKY_BOARD:
                 nhl_add_table_entry_int(L, "tnote", ttmp->tnote);