Fixes #810

* don't recycle input buffer if this leads to growth of the output
buffer

tx_process_join_subscribe() attempted to write response to closed socket.
This patch also fixes diag_raise() with SocketError.

Fixes gh-1624.

Fixes debian/#831361

Free the vclock_to_string() buffer in all cases.

Review fixes:
* revert changes in console.lua, they should be pushed down to
  net.box (it should accept empty passwords)

Previously the URI BNF didn't allow to specify empty
password. There should have been at least one symbol.

Now both user@host and user:@host forms are permitted.

In case of user@host, the password will parsed as nil.
In case of user:@host, the password will be parsed as
empty string.

Fixes #1512

Regression introduced by 9036eeeb

Fill IPROTO_KEY for DELETE and IPROTO_TUPLE for INSERT/REPLACE.

Delete the previous checkpoint in sophia only if we have a new one.

Actually fix the bug and add a test case.

closes gh-1428

Fixed double call of tuple_init_field_map in update and upsert operations, fixed comments of tuple_alloc

Ensure that every box operation can take tuple as key/tupl/operation in
both engines

 * require('console').ac(off) to disable autocompletion;
 * if completion is turned off, TAB key inserts TABs;
 * never fallback to builtin filename completion.