Fix E855 on :lclose

Since 7.3.449 trying to :lclose inside BufWinLeave result in E855:

    $ vi -u /dev/null --noplugin -N
    :autocmd BufWinLeave * if empty(&bt) | lclose | endif
    :lexpr(':1:msg') | lopen | wincmd p | lclose
    E855: Autocommands caused command to abort

    $ vi -u /dev/null --noplugin -N
    :autocmd BufWinLeave * if empty(&bt) | lclose | endif
    :lexpr(':1:msg') | lopen | wincmd p | q
    E855: Autocommands caused command to abort

Another issue with this autocmd is &bt in BufWinLeave may be different from
the buffer being unloaded (this is documented behaviour for BufWinLeave).
Replacing &bt with getbufvar(0+expand('<abuf>'), '&bt') solve this, but
doesn't fix issue with E855 completely (first of above examples with
:lclose is fixed, but second with :q is not fixed).

So, to work around E855 I've changed way to close location-list:
instead of closing it on BufWinLeave, it's closed on BufEnter into
location-list window if it's only buffer in current window.
Merge branch 'master' into E855-on-lclose
Add a check for the error messages variable so that users can specify their own error format.
maven executable option added
detect warnings in jshint

pass `jshint` the `--verbose` option to get 'W' or 'E' indicating
whether something is a warning or an error.

NOTE: this was tested with jshint 1.1.0 installed with `npm install
jshint`
Work with copy of g:syntastic_vala_modules list.
redraw! causes screen flicker in mvim too
recognize flake8 2.0 error output
Added documentation for the g:syntastic_c_checker option
Merge pull request #566 from Chronial/master

flake8 2.0 error parsing
python/flake8: add some backwards compat

make it match E and W for flake < 2.0
Merge pull request #564 from hdoshi/master

Use redraw in mvim
Merge pull request #563 from Lasall/vala-modules-copy

Work with copy of g:syntastic_vala_modules list.
Merge pull request #562 from joshuarh/jshint-warnings

detect warnings in jshint
jshint: add a comment version requirements
Merge pull request #559 from troydm/master

javac checker maven executable option added
Cleanup: a simpler and more efficient approach.
SyntasticChecker: extract out the highlight regex population code
Revert "python/flake8: add some backwards compat"

This reverts commit 0ef513a0a8f14ad8194a3300ec2563761a1334fe.

The cases that I was trying to catch here were already caught further
along in the errorformat
Merge pull request #567 from Chewie/syntastic_c_compiler

Added documentation for the g:syntastic_c_checker option