Implement a helper function to swap space triggers.
Patch by @locker.

Speed up zstd as much as possible.

Update zstd submodule to v1.3.1 version.

Needed to implement SMTP client on the top of libcurl.

See #2704

We can't call initial() from 1.7.6+ because of the space format checks.
Port initial_1_7_5() from 1.8 and use it to boostrap.

Coverity Scan has found a possible bug in a CSV parser - dereferencing
of a null pointer.
But it is not possible. Lets explain:

According to Coverity, the null dereference is in CSV_IN_QUOTES
processing in csv_parse_impl.
But bufp (nullified pointer) can be set to null only in two cases:
CSV_NEWFIELD and CSV_OUT_OF_QUOTES.

In a case of CSV_NEWFIELD the parser sets the state to CSV_LEADING_SPACES and
on a next iteration it sets bufp to not null.

In a case of CSV_OUT_OF_QUOTES the parser can nullify bufp only
if is_end_of_line was true at the end of 'out_of_quotes' processing.
But it means, that is_end_of_line was true at the beginning of
processing too, because CSV_OUT_OF_QUOTES does not modify it.
And at the beggining, if is_end_of_line was true, then the state
is set to CSV_LEADING_SPACES. And on a next iteration bufp are set
to not null.

Closes #2692

Closes #2754

Needed for #2754

sc_space_new return value always is unused. Make sc_space_new
return void.

Needed for #2754

Version is needed in #2754 to ignore space format,
if schema version < 1.7.6.

Needed for #2754

Needed to get format fields during alter in #2754

No semantic changes.

Needed for #2754

Needed for #2754

Needed for #2754

Needed for #2754

Minor renames

Travis images are broken by design.

Closes #2069

Ubuntu Trusty on Travis is buggy.

Fixes #2752

Needed for #946

If the iterator over a merge source was restored to a newer version of
the min key, we must not increment front_id, otherwise the source won't
be advanced on the next iteration, potentially resulting in the same key
returned twice by vy_merge_iterator_next_key(). In the long run, this is
likely to break the cache. Fix this and add an assert() checking that it
never happens.

While we are at it, remove loop from vy_read_iterator_merge_next_key()
that checks that the statement returned by vy_merge_iterator_next_key()
isn't the same as the statement returned to the user last time. The loop
condition should never evaluate to true, which is assured by the new
assert().

Fixes: 61ffe793 ("vinyl: fix read iterator restoration to a newer
version of the same key").

Throw error, if a new name for a fiber in Lua is too long.

Closes #2622

In case of an aggressive optimization coro_unwcontext might be inlined,
so it's should be good to add rax/eax to asm clobber list.

* remove obsolete comments from recovery.cc
* update example lua

* update tarantool man page
* cross-reference tarantool and tarantoolctl pages

The fallthrough attribute with a null statement serves as a fallthrough
statement. It hints to the compiler that a statement that falls through
to another case label, or user-defined label in a switch statement is
intentional and thus the -Wimplicit-fallthrough warning must not trigger.
The fallthrough attribute may appear at most once in each attribute list,
and may not be mixed with other attributes. It can only be used in a switch
statement (the compiler will issue an error otherwise), after a preceding
statement and before a logically succeeding case label, or user-defined
label.

https://developers.redhat.com/blog/2017/03/10/wimplicit-fallthrough-in-gcc-7/