#1 Make u3D Export work for Linux

[SauLus]

U3D seems to only be implemented for OSX and Windows, but not for Linux. Therefore I added a patch that seeks in the appropriate directory.

0: Apply the patch provided
1: download the U3D package from https://sourceforge.net/projects/mathgl/files/ and compile with 'cmake -DSTATIC=ON .'.
2: create directory devel/meshlab/src/meshlab/plugins/U3D_LINUX/
3: create the executable file IDTFConverter.sh in above directory with content:

!/bin/bash

U3D_PATH=/where/you/put/your/U3D
export LD_LIBRARY_PATH=$U3D_PATH:${LD_LIBRARY_PATH}
export U3D_LIBDIR=$U3D_PATH
$U3D_PATH/IDTFConverter $2 $3 $4 $5 $6 $7 $8 $9 ${10} "${11}"

[SauLus]

Make u3D Export work for Linux