lowercase png file extension

[justthefish]

https://bitbucket.org/Zaphide/exerelin/src/09d50895292b6cfdcd746e74459ab6094851829c/graphics/portraits/Nihil.PNG?at=master

Currently extension of this file is in upper case. It causes game crash wile loading on Linux systems - there really is difference between case of letters.

Simple rename to lower case fixes it.

[Kirk Wilson]

(sorry for the late reply, I have been away :) )

Thanks for the report.

I'm not sure the Nihil will be included in the next release version (which will probably come after StarSector 0.6). The current DEV version has all factions removed so it is a non-issue there. If the Nihil are included I will fix the offending file :)

[Kirk Wilson]

No longer required (all mods removed from compilation)