mark bundle files as "files", use luaL_traceback

[truemedian]

Two small changes here:

1. Prepends @ to the chunk name of bundled files so that the shortsrc name becomes bundle:file instead of [string "bundle:file"] in error messages. This is mostly just a convenience thing because the [string ""] just clutters the output on error.

2. Luvi now uses luaL_traceback instead of calling debug.traceback. We have lua53-compat which backfills this function for PUC 5.1 and it's available by default from every other Lua we support.

[truemedian]

The 2 macos failures seem to be a luajit bug also present in master and are unrelated to the applied changes.

[Bilal2453]

What's the difference between luaL_traceback and the current luvi_traceback (debug.traceback)? Or is it just being cleaner?

[truemedian]

debug.traceback almost universally just calls luaL_traceback.

The workaround of going through debug.traceback was only necessary because:

1. PUC Lua 5.1 doesn't have luaL_traceback
2. the 5.3-compat luaL_traceback doesn't print luajit ffunc names (the "builtin#40" entries)