How to reproduce:

1. Open the editor
2. Look at the icons for these functions:
- All of the scene manipulation tool icons
- Tool Handle option icons
- Play/Pause/Frame buttons
- Magnifying glass icons in the search boxes
- The Services icon (the cloud)
- The tab icons for Hierarchy, Game, Project, Profiler, Inspector, Animation, Asset Store and Navigation windows
- The scene view Lighting, Audio and the Effects icons
- See also the attached screenshots

- They all appear to be lower resolution than the other icons
- The icons that consist of no curved lines (such as the Lighting and Occlusion tab icons) appear fine

- Reproduced in Version 5.4.0b11 (323b0238353b)
- Retina support was not available prior to 5.4