[connector][perl] AnyEvent support. Continuation support. Limit = max_sint32 by default. primary_key_index option.

Conflicts:
	connector/perl/lib/MR/SilverBox.pm

tnt_stream_reqid()

Use the index iterator API in memcached.m,
instead of hard-coded access to index internals,
which broke index abstraction.

This (temporarily) can (somewhat) break expire
in presense of SELECT command against memcached namespace,
since SELECT uses the same iterator.

Hopefully, it's only temporary, since we'll soon
be able to have more than one independent generic iterator
over the same index.

Do not pre-allocate Index object.

Fix valgrind errors.

A pre-requisite patch for turning Index into an Object:

Extract key description into an own structure, struct key.

Introduce key_config function, which
transfers configuration from confetti structure
into struct key.

This allows to decouple index construction from
key construction -- something you need
if you want a virtual constructor for index.