- Fix plugin detection:
We need USE_FHS_PLUGIN_PATH=yes so tiled finds the plugins and
doesn't look relative to the executables path.
Without this exporting to lua, json etc never worked.

- Update to version 0.18.0:
* Added Layer via Copy/Cut actions
* Added support for Paste in Place action for tile layers
* Added context menu to change custom property type (by Dmitry Hrabrov)
* Added support for higher precision for custom floating point properties
* Added %mappath variable to commands (by Jack Roper)
* Added snapping to pixels (by Mamed Ibrahimov)
* Added right-click to clear the tile selection
* Added a context menu action to reset the size of tile objects
* Added exporter for Game Maker Studio room files (by Jones Blunt)
* Added Move Up/Down buttons to Objects view (by iskolbin)
* Added pixel coordinates to status bar for object tools (by iskolbin)
* Added Sticker Knight platformer example (by Ponywolf)
* tmxrasterizer: Added --size argument and support local file URLs
* tmxrasterizer: Use smooth pixmap transform by default
* Linux: Register tmxrasterizer as thumbnail generator for TMX files
* Allow scrolling past map edges with mouse wheel
* Enabled HiDpi scaling and improved the quality of some icons
* Reversed the order of the objects in the Objects view
* JSON plugin: Added Node.js support to the JavaScript export
* Updated TMX schema definition (by assofohdz)
* Fixed unfinished objects getting saved
* Fixed OpenGL rendering mode when application is scaled (HiDpi screens)
* Fixed Remove and Rename actions for predefined properties
* Windows: Fixed console output