Omnisharp: smarter solution file finder

When loading the Omnisharp server, YCM tries to find a suitable solution
file to feed it. Instead of giving up when finding multiple solution
files, it now tries to find one named like the edited files' folder at
the solution level, e.g. if we have bla/Project.sln and we are editing
bla/Project/Folder/Whatever/File.cs, we use bla/Project.sln.
Unit test for Omnisharp's smarter solution finder
Unit tests for Omnisharp's smarter solution finder
Merge github.com:nop00/YouCompleteMe
Small stylistic changes
Merge pull request #680 from nop00/master

Omnisharp: smarter solution file finder
Fix --system-libclang on Ubuntu/Debian
Merge pull request #713 from LeszekSwirski/fix-ubuntu-syslibclang

Fix --system-libclang on Ubuntu/Debian
Only notify about a server crash once

Fixes #715
Merge pull request #717 from blueyed/notify-about-crash-once-issue-715

Only notify about a server crash once
Not using Syntastic lazy redraw anymore

This gets rid of the annoying flashing (issue #669), but reverts the workaround
for a rare Vim crash bug (issue #593). We can't have both. Update to latest Vim
to not get the crash bug.

Fixes #669.
New entry to FAQ about Vim crash

Happens sometimes when users tab through the completion menu. Related to #593.
Updating to latest Jedi dev branch

This should finally fix #599.
Updating vimdoc from README
Check for libc++ before using it.

Fixes #731.
Changed HEAD of third_party/argparse (Create gitignore file).
Merge pull request #736 from dzhioev/master

Changed HEAD of third_party/argparse (Create gitignore file).
Try to cleanup files only if they stil exist

Fixes #738
Better handling of unknown extra conf files

Previously, we'd implicitly turn off future notices about unknown extra conf
files if we already raised one exception about it. This breaks when the user
ends up not receiving the "unknown extra conf, load?" message.

Now we only turn off the notice as a result of the user saying "don't load this"
so that if the first request fails to reach them, they'll get a second (and
third etc) request about it.

Fixes #615
Solution to issue #708