libports: add ICU library

The ICU (International Components for Unicode) library is needed for Qt5.

Fixes #828.
noux: construct new child only if binary is valid

If a script is executed which uses a interpreter that does not exist the
construction of the child fails and potentially leaks memory because the
wrong delete operator is called.
Therefore the binary dataspace of the script and the binary dataspace of
the interpreter are now checked before a new child will be created.

Fixes #812.