The client now just caches a simple list of gag names that the server
sends it via a new IPC_GAGLIST message.

🔥🔥🤷🔥🔥

Requires build flag tweaks to make container_of() work. (-pedantic
doesn't make much sense with -std=gnu99 anyway).

Mainly for readability but also removes a duplicate strlen() call on the
input text.

Use duk_pcompile_string_filename() and duk_pcall() instead of
duk_peval() so we get the filename in js backtraces:

  mwjs error: RangeError: execution timeout
      at [anon] (duktape.c:72259) internal
      at fooCmd (.mw-script/mw.js:20) preventsyield

duktape has no equivalent of JS_IsRunning() so use the state of the
timeout tracking bits to approximate it.

And clean the duktape directory with 'make clean' as it builds fast
enough.

Since duktape provides a nice way to concatenate strings, use that
instead of the urldata() function.

We don't want user scripts to depend on the Duktape object