…is needed in case the ICU library is not installed.

Change CMake related files that Boost can also be build on Mac OSX. There have been problems with linking on Mac OSX
since there is no default "lazy linking" on this platform. There was alos a problem to compile the mpi library since some
of the parameters haven't been passed correctly.

…This is needed on linux (at least on Ubuntu) because there is no separate iconv library but the functionality is included in the libc. If the functionality is not found in libc look for a separate library.

…inst the shared libboost_unit_test_framework which has no main function. If one neeeds a main function from boost one has to link against the static version of this library. There is also only a static version of the test_exec_monitor library, so one has to link the executables against this version.