Avoid unnecessary calls to wildignore

This is significantly faster on large file lists

Originally submitted at: https://github.com/wincent/Command-T/pull/96

Signed-off-by: Greg Hurrell <greg@hurrell.net>
Drop unneeded `else` clause

None of the callers require strict boolean-ness, so let `nil`
false-yness suffice.
Update specs for recent wildignore changes
doc: update HISTORY section
Merge branch 'pfhayes/wildignore' into next

Originally submitted at: https://github.com/wincent/Command-T/pull/96

* pfhayes/wildignore:
  doc: update HISTORY section
  Update specs for recent wildignore changes
  Drop unneeded `else` clause
  Avoid unnecessary calls to wildignore