QwtSymbol::Pixmap and pinpoint translations fixed, when being cached


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1981 29e17f8d-cf37-471e-a288-72cc03a76eda
avoiding of pointless tick label calculations for multiturn knobs


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1984 29e17f8d-cf37-471e-a288-72cc03a76eda
performance issues with rounded scales


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1989 29e17f8d-cf37-471e-a288-72cc03a76eda