lib: istream: Allow switching to a specific ioloop.

Updated copyright notices to include the year 2018.

lib: istream-multiplex - Return error if the last packet wasn't fully read

global: Use i_stream_read_memarea() wherever possible

global: Add flags parameter to i_stream_create() and set it to 0 This just changes the API - the following changes add the new flag.

global: Use i_stream_free_buffer() instead of freeing w_buffer directly

lib: istream-multiplex - Minor optimization There's no need to find channel when we already know it. This also helps static analyzers to understand that req_channel can't be NULL.

lib: istream-multiplex - Forward i_stream_switch_ioloop() to parent Most istreams do this because istream_private.parent is set to the parent stream, but this can't be done with istream-multiplex. The main problem with attempting to do the same with istream-multiplex is that the different channels don't share the same I/O. Just because one channel received data doesn't mean that other channels received any data. (It would be possible to solve this by implementing a new method that allows overriding i_stream_set_io(), but I'm not sure if that's a good idea either.)

lib: istream-multiplex - remove dead assignment

lib: istream-multiplex - Minor code cleanup Avoid propagating the error twice, and avoid any confusion about what "got" actually contains.

lib: Add multiplex stream support This allows having multiple channels of data in single stream.