Fix narrowing behavior
List symlink location, not real file loc, in unite

When performing (fuzzy) file searches from the current directory
downwards, I imagine most users would prefer to filter on the symlink's
path rather than the actual file location. E.g. if I symlink
/Users/me/Dropbox/code/project1 to /Users/me/src/python/django/project1,
and am currently in /Users/me/src/python, I'd want to be able to use
'django' in the fuzzy search string, and wouldn't care in the least
about the 'Dropbox' part.
Fix s:clear_previewed_buffer_list() problem
Fix #491 ignore E325 in action
Merge pull request #667 from chrischambers/master

List symlink location, not real file location, in unite buffer
Remove unused variable
Fix errors
Fix documenation
[WIP] Improved file_rec/async

Note: applied vimproc.vim/improve-readwrite