Make top level git path work with Cygwin/MSYS2

Cygwin and MSYS2 used Git for Windows which returns a windows path which
doesn't work in vim.
This change looks for the presence of the cygpath executable which
if present indicates its running under Cygwin or MSYS2.
  It then uses cypath is to convert the windows path to a compatible
  path.

autoload/magit/git.vim

@@ -52,9 +52,9 @@ function! magit#git#is_work_tree(path)
 	try
 		call magit#utils#chdir(a:path)
 		let top_dir=system(g:magit_git_cmd . " rev-parse --show-toplevel")
-    if ( executable("cygpath") )
-      let top_dir = magit#utils#strip(system("cygpath " . top_dir))
-    endif
+		if ( executable("cygpath") )
+			let top_dir = magit#utils#strip(system("cygpath " . top_dir))
+		endif
 		if ( v:shell_error != 0 )
 			return ''
 		endif
@@ -75,10 +75,10 @@ function! magit#git#set_top_dir(path)
 			let top_dir=magit#utils#strip(
 						\ system(g:magit_git_cmd . " rev-parse --show-toplevel")) . "/"
 			let git_dir=magit#utils#strip(system(g:magit_git_cmd . " rev-parse --git-dir")) . "/"
-      if ( executable("cygpath") )
-        let top_dir = magit#utils#strip(system("cygpath " . top_dir))
-        let git_dir = magit#utils#strip(system("cygpath " . git_dir))
-      endif
+			if ( executable("cygpath") )
+				let top_dir = magit#utils#strip(system("cygpath " . top_dir))
+				let git_dir = magit#utils#strip(system("cygpath " . git_dir))
+			endif
 		catch 'shell_error'
 			call magit#sys#print_shell_error()
 			throw 'set_top_dir_error'