Fix Vim indent regressions from #13600.

The change in #13600 was incorrect, containing a bad regular expression;
inside an indent function, errors are silently ignored (and the ``~=``
operation will return 0), so it just always failed, causing the cases
that were supposed to be caught to not be caught and making things like
the ``match`` example shown above or struct field definitions regress.

I have fixed the regular expression to what it should have been. This is
still imperfect, of course, not handling cases like where the first
argument to a function is a function call (``foo(bar(),``), but it'll do
for now.
auto merge of #13729 : chris-morgan/rust/fix-vim-indent, r=alexcrichton

The change in #13600 was incorrect, containing a bad regular expression;
inside an indent function, errors are silently ignored (and the ``~=``
operation will return 0), so it just always failed, causing the cases
that were supposed to be caught to not be caught and making things like
the ``match`` example shown above or struct field definitions regress.

I have fixed the regular expression to what it should have been. This is
still imperfect, of course, not handling cases like where the first
argument to a function is a function call (``foo(bar(),``), but it'll do
for now.

----

I have a general request to make of reviewers about any changes made to `src/etc/vim`: **please tell me**. As a general rule I want to review them. (I’ll make an exception for changes the prelude; it needs fixing from time to time when some people don’t update the syntax file, anyway.)

cc @brandonw
native: Remove unused and untested UnixDatagram
std: Add timeouts to unix connect/accept

This adds support for connecting to a unix socket with a timeout (a named pipe
on windows), and accepting a connection with a timeout. The goal is to bring
unix pipes/named sockets back in line with TCP support for timeouts.

Similarly to the TCP sockets, all methods are marked #[experimental] due to
uncertainty about the type of the timeout argument.

This internally involved a good bit of refactoring to share as much code as
possible between TCP servers and pipe servers, but the core implementation did
not change drastically as part of this commit.

cc #13523