Add osmesa to help texts

Author: LinusDierheimer

src/data/config.txt

@@ -159,7 +159,7 @@
 
 # GL option
 # Sets with opengl context creation library to use
-# Must be either auto, egl or glx
+# Must be either auto, egl, glx or osmesa
 # Default is auto.
 #--gl auto
 

src/data/help.txt

@@ -150,7 +150,7 @@ Module specific options:
     --localip-show-loop <?value>: Show loop back addresses (127.0.0.1) in local ip module. Default is false
     --public-ip-timeout:          Time in milliseconds to wait for the public ip server to respond. Default is disabled (0)
     --player-name:                The name of the player to use
-    --gl <value>:                 Sets the opengl context creation library to use. Must be auto, egl, or glx. Default is auto
+    --gl <value>:                 Sets the opengl context creation library to use. Must be auto, egl, glx or osmesa. Default is auto
 
 Parsing is not case sensitive. E.g. "--lib-PCI" is equal to "--Lib-Pci"
 If a value starts with a ?, it is optional. "true" will be used if not set.