mcs (mono) on Windows fails to lint

TLDR: You need to make a batch file to use mcs linter on Windows

## Information

**VIM version**

VIM - Vi IMproved 8.0 (2016 Sep 12, compiled May 1 2017 22:02:48)
MS-Windows 64-bit GUI version with OLE support

Operating System: Win10

### :ALEInfo

Current Filetype: cs
Available Linters: ['mcs', 'mcsc']
Enabled Linters: ['mcs', 'mcsc']
Linter Variables:

let g:ale_cs_mcs_options = ''
let g:ale_cs_mcsc_assemblies = []
let g:ale_cs_mcsc_assembly_path = []
let g:ale_cs_mcsc_options = ''
let g:ale_cs_mcsc_source = ''
Global Variables:

let g:ale_echo_cursor = 1
let g:ale_echo_msg_error_str = 'Error'
let g:ale_echo_msg_format = '%code: %%s'
let g:ale_echo_msg_warning_str = 'Warning'
let g:ale_enabled = 1
let g:ale_fix_on_save = 0
let g:ale_fixers = {}
let g:ale_keep_list_window_open = 0
let g:ale_lint_delay = 200
let g:ale_lint_on_enter = 1
let g:ale_lint_on_save = 1
let g:ale_lint_on_text_changed = 'normal'
let g:ale_linter_aliases = {}
let g:ale_linters = {}
let g:ale_open_list = 0
let g:ale_set_highlights = 1
let g:ale_set_loclist = 1
let g:ale_set_quickfix = 0
let g:ale_set_signs = 1
let g:ale_sign_column_always = 0
let g:ale_sign_error = '>>'
let g:ale_sign_offset = 1000000
let g:ale_sign_warning = '--'
let g:ale_statusline_format = ['%d error(s)', '%d warning(s)', 'OK']
let g:ale_warn_about_trailing_whitespace = 1
Command History:

(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs
(executable check - failure) mcs

## What went wrong

Linting doesn't work. Vim doesn't think I have mono. I installed with [their instructions](http://www.mono-project.com/docs/getting-started/install/windows/). The "Mono 64-bit (no GTK#)" installer doesn't let you choose a destination, it just goes into program files. Added that to vimrc:

let $PATH = $PATH . ';"C:/Program Files/Mono/bin/"'

But I get the above failure.

Checking from vim:

:echo executable('mcs')
0

:!mcs --version
C:\WINDOWS\system32\cmd.exe /c (mcs --version)
Mono C# compiler version 5.8.0.0

So I can run it, but vim doesn't know about it.

## Workaround

Create a batch file:
C:/bin/mcs.cmd

@echo off
call "%ProgramFiles%\Mono\bin\mcs.bat" %*

Add c:/bin to your PATH.

Restart vim.

It works!

## Conclusion

It doesn't seem that vim can't look at stuff in Program Files (works with TortoiseSVN executables). I think it's because Mono has a bash `mcs` file and a batch `mcs.bat`, but I don't understand how that breaks things. Renaming `mcs` to `mcs_other` seems to also fix it. Editing the linter to use mcs.bat didn't seem to fix it.

I know vim searches for multiple extensions (`:help executable()`), so I guess that's related:

:Verbose ec $PATHEXT
.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.wlua;.lexe

I'm happy to use the batch file. I'm not sure how you'd attempt to fix this, but I hope this info is useful to someone else.