fix for Qt 4.8.7 <-> Boost conflict

[samarth-robo]

Qt 4.8.7 has a conflict with Boost 1.65.1. Even though graspit_interface does not use Boost, other ROS libraries do, and it is pulled in. This causes the following error when compiling:

[ 98%] Built target graspit_interface_generate_messages
/usr/include/boost/predef/language/stdc.h:52: Parse error at "defined"
graspit_interface/CMakeFiles/graspit_interface.dir/build.make:81: recipe for target 'graspit_interface/include/moc_graspit_interface.cxx' failed
make[2]: *** [graspit_interface/include/moc_graspit_interface.cxx] Error 1
CMakeFiles/Makefile2:973: recipe for target 'graspit_interface/CMakeFiles/graspit_interface.dir/all' failed
make[1]: *** [graspit_interface/CMakeFiles/graspit_interface.dir/all] Error 2
Makefile:159: recipe for target 'all' failed
make: *** [all] Error 2
Invoking "make -j16 -l16" failed

See discussion here: LARG/HFO#79. Following @jespestana's answer there, I modified the CMakeLists.txt, which fixes the issue and checked that graspit_commander's py.test finishes successfully.