Optimize FaustFactory.wht() C++ backend; only one factor is really created in...

Optimize FaustFactory.wht() C++ backend; only one factor is really created in memory because all others are in fact the same.

If a hadamard tranform was created calling FaustFactory.wht(n), then the space used is now divided by n compared to what it was before this commit.

This commit is related to issue #17.