fix for recent update

[sebaselizeche]

fixes #176

[joedwards32]

Thank you for your contribution!

On this occasion, I think the approach in #179 is more correct:

• Doesn't expand library search path until the additional paths actually exist (doesn't change functionality, but is neater)
• Appends to the path rather than prepending, maintaining existing library selection if duplicates exist
• Fixes libserver_valve too, which requires soft linking as so must be done in the entry script