Support unusual characters in file and directory names (#868)

* Use a delimiter in node to separate file/dir name from the rest.

* Switch warning message to use nerdtree#deprecated function.

* Compress the space between the tree symbols and the node.

* Include the delimiter when calculating indent or getting filename.

* Don't need to strip leading delimiter. It will already be gone.

* Simplify the way the delimiter is being used.

I don't know what I was thinking. The delimiter doesn't need to be used
to separate every indicator on the node's text, ie.

Bad:    Tree|GenericFlags|Filename|ExecutableFlag|Link|ReadonlyFlag
Better: Tree GenericFlags|Filename|ExecutableFlag Link ReadonlyFlag

This was unnecessary, given that we're only interested in the filename.
So, just one pair of delimiters is all we need. That greatly simplifies
the _stripMarkup function, and restores a bunch of other statements to
what they already are in the master branch.

* Add syntax highlighting to conceal the delimiter

* Put a if has("conceal") check around the syntax statement using it.

* Make concealment work correctly for LinkFile and readonly files.

* Use highlight Ignore if conceal isn't available.

This is probably the best we can do, especially if some other character
must be used in place of nbsp.

* Make the regex better match the original, but more compact.

It was allowing 2+ spaces, instead of only 1+.

* Fix the syntax highlighing of delimiters around NERDTreeExecFile.

* Bug fix: Parse . and .. from path string with trailing slash.

* Fix unresponsive cascaded directories.

Using ':' as a more visible delimiter, when directories are cascaded,
the line appears in NERDTree like so:

▾ :lib/::nerdtree/:

Before this commit, the s:UI._stripMarkup function was leaving the
internal delimiters in place (lib/::nerdtree/). Now they are removed,
resulting in a valid path (lib/nerdtree/).

* Use .= to shorten statement. Use clearer substitutes to get node name.

* Remove node delimiters that terminate the line.

* If flags are needed after the node name, then put another delimiter
before them.
* When joining directory nodes for cascaded display, strip off the
delimiter from the child node(s).
* Remove the unnecessary substitution of doubled intermediate
delimiters, since they're not in there anymore.

* DRY up the addition of the 2nd delimiter, and use only 1 for all tags.

plugin/NERD_tree.vim

@@ -86,6 +86,9 @@ let g:NERDTreeOldSortOrder = []
 
 call s:initVariable("g:NERDTreeGlyphReadOnly", "RO")
 
+" ASCII 160: non-breaking space used to delimit items in the tree's nodes.
+call s:initVariable("g:NERDTreeNodeDelimiter", "\u00a0")
+
 if !exists('g:NERDTreeStatusline')
 
     "the exists() crap here is a hack to stop vim spazzing out when