Fix {'keepopen':0} in NERDTreeCustomOpenArgs (#1217)

* Replace #and() with two more-specific functions.

* Push NERDTreeQuitOnOpen checking earlier in the call stack.

* Fix bug in `go` key for file bookmarks. It was behaving like `gs`.

* Fix the `o` mapping for bookmark nodes and the g:NERDTree reference.

* Use get() function to shorten if statement logic.

* Update version number in change log.

* Remove obsolete reference to MERDTreeQuitOnOpen in comment.

autoload/nerdtree.vim

@@ -30,6 +30,16 @@ endfunction
 " SECTION: General Functions {{{1
 "============================================================
 
+" FUNCTION: nerdtree#closeTreeOnOpen()
+function! nerdtree#closeTreeOnOpen() abort
+    return g:NERDTreeQuitOnOpen == 1 || g:NERDTreeQuitOnOpen == 3
+endfunction
+
+" FUNCTION: nerdtree#closeBookmarksOnOpen()
+function! nerdtree#closeBookmarksOnOpen() abort
+    return g:NERDTreeQuitOnOpen == 2 || g:NERDTreeQuitOnOpen == 3
+endfunction
+
 " FUNCTION: nerdtree#slash() {{{2
 " Return the path separator used by the underlying file system.  Special
 " consideration is taken for the use of the 'shellslash' option on Windows
@@ -46,28 +56,6 @@ function! nerdtree#slash() abort
     return '/'
 endfunction
 
-"FUNCTION: nerdtree#and(x,y) {{{2
-" Implements and() function for Vim <= 7.4
-function! nerdtree#and(x,y) abort
-    if exists('*and')
-        return and(a:x, a:y)
-    else
-        let l:x = a:x
-        let l:y = a:y
-        let l:n = 0
-        let l:result = 0
-        while l:x > 0 && l:y > 0
-            if (l:x % 2) && (l:y % 2)
-                let l:result += float2nr(pow(2, l:n))
-            endif
-            let l:x = float2nr(l:x / 2)
-            let l:y = float2nr(l:y / 2)
-            let l:n += 1
-        endwhile
-        return l:result
-    endif
-endfunction
-
 "FUNCTION: nerdtree#checkForBrowse(dir) {{{2
 "inits a window tree in the current buffer if appropriate
 function! nerdtree#checkForBrowse(dir) abort