TextureSource has a list of textures to delete (m_texture_trash) so this
provides a proper, non-hacky way to delete RTT textures. Also, the prior,
hacky way of deleting them seems to be broken (see pull request #803).
To avoid header file clutter by repeating the same long list of
arguments over and over again, store the arguments of
generateTextureFromMesh in a struct called TextureFromMeshParams.
Also fix issue #782 (Only use bilinear (and others) on item textures
when settings allow it).
This causes textures to be deleted before they are no longer accessed,
resulting in a segmentation fault. This needs to be rewritten in such a way
that textures are deleted when the client disconnects from a server.
This reverts commit 41c00e87d42580881d8c7001f39014814e3b55f2.
