spectrogram test code removed


git-svn-id: svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1@2107 29e17f8d-cf37-471e-a288-72cc03a76eda
doxygen fixes


git-svn-id: svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1@2111 29e17f8d-cf37-471e-a288-72cc03a76eda