Memory / CPU script limits

(from [e203f17e196b811162a66a6446180513c0691ea5]) API for limiting resource usage.

You can now enforce crude resource usage limits for scripts executing in the JS VM. Its not overly granular and has some caveats, but it appears to work.

To limit the time a script can run:

>>> rt = spidermonkey.Runtime()
>>> cx = rt.new_context()
>>> cx.max_time(5) # Specified in seconds, returns the previous value.
0
>>> cx.execute("while(true) {}")
...
RuntimeError

To limit the amount of memory is similar:

>>> rt = spidermonkey.Runtime()
>>> cx = rt.new_context()
>>> cx.max_memory(10000) # Specified in bytes, returns the previous value.
0
>>> cx.execute("var f = []; var b = 100000; while(b-- > 0) f.push(b*0.9)")
...
RuntimeError

At the moment this looks like its limiting resources per context when in reality its per runtime. So if you limit to usage on a context, and some other script in the context is running above that limit, the limited context will fail.

You can also get the current values without setting:

>>> cx.max_time(10)
...
>>> cx.max_time()
10
>>> cx.max_memory(10000)
...
>>> cx.max_memory()
10000

Some minor tweaks to make the memory limit specified on the Runtime and to improve the reported errors to follow shortly.

[#12 Memory / CPU script limits] http://github.com/davisp/python-...

(from [584ba6f0e3e7078d4a0eeed0c4094a31703a643a]) Updates to the build system.

Linking against the library works, but importing spidermonkey kills the Python VM because of an unresolved symbol. Can't figure out if this is just OS X's build of libmozjs or if I'm missing a flag.

[#12 Memory / CPU script limits] http://github.com/davisp/python-...

(from [c29ad86edfb992056dbc4b9f1c10f909149abe04]) Updated the README. Thanks Mark Lee.

[#12 Memory / CPU script limits] http://github.com/davisp/python-...