File browser UI tweaks.
Fix up parent path handling for windows.
Add ignores for EBUSY, EPERM errors.
Normalize windows paths in history.
Merge pull request #602 from mapbox/browser-tweak

Browser tweak
Merge branch 'master' into history-normalize-winpath
Use the right sep value when opening files.
Merge pull request #603 from mapbox/history-normalize-winpath

Normalize history paths
Merge branch 'master' into atom-child