generalize ctdFindDescents(), rename ctdFindProfiles()
ctdFindProfiles(): experiment with smooth.spline method
remove debuggging line
make [[ operator return NULL if item not found

This mimicks the list behaviour
ctdFindProfiles() approaching a stable design
ctdFindProfiles() improvements
swPressure() added
swPressure() bug fixed
ctdFindProfiles(): change some arguments
ctdFindProfile() improvements
subset.ctd() added [issue 326]
subset.lisst() added [issue 326]
subset.tdr() added [issue 326]
subset.sealevel() added [issue 326]
generalize recently added subset.* functions
using S4 methods for subset()
doing subset() with S4
improve stationID values for Gulf Stream
processingLogShow() now returns invisible
plot.section() now finds best avail coastline