Add a new cnse.fetchscript, which first checks for an absolute path,

then looks in the scripts subdirectory, then in the current directory.
cnse.fetchfile_absolute now checks for an absolute path, then calls
nmap_fetchfile if that fails (and no longer looks in scripts/). Use
cnse.fetchscript when accessing files that should be in the scripts
subdirectory.

nse_main.cc

@@ -257,6 +257,7 @@ static void open_cnse (lua_State *L)
 {
   static const luaL_Reg nse[] = {
     {"fetchfile_absolute", fetchfile_absolute},
+    {"fetchscript", fetchscript},
     {"dir", nse_readdir},
     {"nsock_loop", nsock_loop},
     {"key_was_pressed", key_was_pressed},