fix trust -search for Ub >=18
Add a msg when Xterm is null, gdb cannot be used for TRUST parallel computation
Add proper exit if valgrind test fails
Use LAPACK installed by trust for Gmsh
ICoCo Tutorial correction
update RELEASE_NOTES
flex-2.6.4 cannot be installed on Ub18/gcc-7.5. Downgrading it to 2.6.0
flex-2.6.4 cannot be installed on Ub18/gcc-7.5. Downgrading it to 2.6.0