lib: Add i_stream_get_root_io() and use it to deduplicate code

lib: istream: Allow switching to a specific ioloop.

lib: Add i_stream_get_last_read_time()

lib: i_stream_read() - Use snapshots This guarantees that data returned by i_stream_get_data() won't be freed until the next i_stream_read() returns >0. This is mainly important, because often the error handling for <=0 doesn't update the buffer pointers correctly and it leads to complicated bugs where already freed memory is attempted to be read (but never written).

lib: Add ISTREAM_CREATE_FLAG_NOOP_SNAPSHOT flag

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.

lib: Add i_stream_try_alloc_avoid_compress()

lib: Add istream.snapshot() method for referencing the current memarea It will be used by following commits.

lib: Use memarea for default istream memory allocations.

lib: Add i_stream_free_buffer() to free i_stream_*alloc()ed memory

global: unsigned int:1 -> bool:1 perl -i -pe 's/unsigned int ([^,:;]+):1;/bool $1:1;/' **/*.[ch]

lib: Changed istream.abs_start_offset to be relative start_offset i_stream_get_absolute_offset() walks through the stream's parents to get the absolute offset. This allows streams to change their start_offset after they have already created (e.g. istream-metawrap).

lib: Added i_stream_set_persistent_buffers()

Added io_add_istream() and related functionality for combining the ioloop/istream. The idea here is that it's possible to implement asynchronous istreams when there isn't a file descriptor that can be used to reliably receive updates.

istream: Added i_stream_init_parent() to lazily initialize the parent stream.

istream: Added internal try_alloc_limit to limit size returned by i_stream_try_alloc() This was required by the previous SSL change.

i_stream_stat() API changed. This fixes also one missing error check.

Added i_stream_last_line_crlf()

istreams: Added default stat() implementation for filter streams.

istreams: Added default seek() implementation for seekable streams.

Added i_stream_alloc()

istreams: Renamed i_stream_get_buffer_space() to i_stream_try_alloc()

Avoid using (void)s by adding ATTR_NOWARN_UNUSED_RESULT attributes and other ways.

Marked functions parameters that are allowed to be NULL. Some APIs were also changed. The non-obvious APIs where NULL parameter was changed to "" are master_service_init() and auth_master_user_list_init(). These checks can currently be enabled only on a patched clang: http://llvm.org/bugs/show_bug.cgi?id=6786

Renamed lib/*-internal.h files to lib/*-private.h for consistency.