Added Case Sensitive Move Operation via newly introduced flag NERDTreeCaseSensitiveFS (#1375)

* Added NERDTreeCaseInsensitiveFS option.

* check against g:NERDTreeCaseInsensitiveFS with path.equals method

* Fixed issues in comments and added nerdtree#runningMac

* Using nerdtree#runningMac instead of manual checks for mac

* Better implementation

* Updated documentation

* Added notice about the flag

* Updated the documentation

* Added support for g:NERDTreeCaseSensitiveFS = 3

* Better comments

* Exported caseSensitiveFS check as a function

autoload/nerdtree.vim

@@ -198,16 +198,42 @@ function! nerdtree#postSourceActions() abort
     runtime! nerdtree_plugin/**/*.vim
 endfunction
 
-"FUNCTION: nerdtree#runningWindows(dir) {{{2
+"FUNCTION: nerdtree#runningWindows() {{{2
 function! nerdtree#runningWindows() abort
     return has('win16') || has('win32') || has('win64')
 endfunction
 
-"FUNCTION: nerdtree#runningCygwin(dir) {{{2
+"FUNCTION: nerdtree#runningCygwin() {{{2
 function! nerdtree#runningCygwin() abort
     return has('win32unix')
 endfunction
 
+"FUNCTION: nerdtree#runningMac() {{{2
+function! nerdtree#runningMac() abort
+    return has('gui_mac') || has('gui_macvim') || has('mac') || has('osx')
+endfunction
+
+" FUNCTION: nerdtree#osDefaultCaseSensitiveFS() {{{2
+function! nerdtree#osDefaultCaseSensitiveFS() abort
+    return s:osDefaultCaseSensitiveFS
+endfunction
+
+" FUNCTION: nerdtree#caseSensitiveFS() {{{2
+function! nerdtree#caseSensitiveFS() abort
+    return g:NERDTreeCaseSensitiveFS == 1 ||
+                \((g:NERDTreeCaseSensitiveFS == 2 || g:NERDTreeCaseSensitiveFS == 3) &&
+                \nerdtree#osDefaultCaseSensitiveFS())
+endfunction
+
+"FUNCTION: nerdtree#pathEquals(lhs, rhs) {{{2
+function! nerdtree#pathEquals(lhs, rhs) abort
+    if nerdtree#caseSensitiveFS()
+        return a:lhs ==# a:rhs
+    else
+        return a:lhs ==? a:rhs
+    endif
+endfunction
+
 " SECTION: View Functions {{{1
 "============================================================
 
@@ -246,4 +272,12 @@ function! nerdtree#renderView() abort
     call b:NERDTree.render()
 endfunction
 
+if nerdtree#runningWindows()
+    let s:osDefaultCaseSensitiveFS = 0
+elseif nerdtree#runningMac()
+    let s:osDefaultCaseSensitiveFS = 0
+else
+    let s:osDefaultCaseSensitiveFS = 1
+endif
+
 " vim: set sw=4 sts=4 et fdm=marker: