`R CMD check` warning: "no visible global function definition"

While checking synapter via `R CMD check` I get the following warnings:

    .filterIntensity: no visible global function definition for ‘fData’
    .filterIntensity: no visible global function definition for ‘fData<-’
    .getSpectrum: no visible global function definition for ‘assayData’
    .plotCxRow : <anonymous>: no visible global function definition for ‘fData’
    coerce,Synapter-MSnSet: no visible global function definition for ‘fData’
    coerce,Synapter-MSnSet: no visible global function definition for ‘featureNames<-’

IMHO you have to export overloaded methods as well.
That's why I added `assayData`, `fData` and `featureNames` to `NAMESPACE` but maybe more methods are affected.