util.dbuffer: Fix traceback when :collapse() is called on empty buffer

util.dataforms: Add more XEP-0211 media element test coverage

util.dataforms: Convert media element sizes to avoid error on Lua 5.3 The stanza API does not accept number values and threw an error due to the height and width attributes of the media element (XEP-0221). This part had no test coverage previously, explaining why it was not discovered until now.

net.http.errors: Add new module for converting net.http errors to util.error objects

mod_net_multiplex: Set read size/mode to that of the target listener Otherwise it would use the configured buffer size, or previously '*a'. Using the read size set by the listener seems more sensible.

mod_net_multiplex: Read no more than the max buffer size setting Otherwise the '*a' read mode applies, which under certain circumstances can read infinite amounts of data into memory.

mod_http: Add way to signal that a module supports streaming uploads Fixes #726 API: module:provides("http", { streaming_uploads = true; route = { PUT = function (event) event.request.body_sink = io.tmpfile(); return true; end } })

net.http.parser: Allow specifying sink for large request bodies This enables uses such as saving uploaded files directly to a file on disk or streaming parsing of payloads. See #726

net.http.parser: Switch to util.dbuffer for buffering incoming data This is primarily a step towards saving uploads directly to files, tho this should hopefully be more efficient than collapsing the entire buffer to a single string every now and then.

Merge 0.11->trunk