Made XPUI.nsh add the Plugin and Include directories relative to XPUI_SYSDIR to make detached installations work better.
[Settings]
NumFields=2
[Field 1]
Type=label
Text=Instal Options Page C
Left=0
Right=-1
Top=0
Bottom=10
[Field 2]
Type=checkbox
Text=Display a MessageBox
Left=0
Right=-1
Top=30
Bottom=40
State=1