Internal functions that determine OS-specific path in which modules might be located.
rsaga.get.modules.path(sysname = Sys.info()["sysname"], saga.path, root, cmd)
character: name of the operating system, determined by default by base::Sys.info()
: e.g., "Windows"
, "Linux"
, "Darwin"
(for Mac OSX), or "FreeBSD"
character: path with SAGA GIS binaries, as determined (e.g.) by rsaga.default.path
root path to SAGA GIS installation
name of the SAGA command line program