Option "Keep Single Instance" is not working for *.inc files

[syanenko]

Summary

Option "Keep Single Instance" is not working for *.inc files.

POV-Ray Version

• Incarnation: POV-Ray for Windows
• Affected build version: 3.8-beta.2

Runtime Environment

• Operating system: Windows 7
• Hardware architecture: x86-64
• CPU model: Intel Core i5 @ 2.50GHz

Steps to Reproduce

1. Open POV-Ray environment
2. Select *.inc file in Explorer

Expected Behavior

File opens in running instance

Actual Behavior

New instance of POV environment starts