Draft code for additional vtypes: Paths, with appropriate open channels as internal rep.
Modified the checks for wfile/wchan to allow non-existing files which can be created (per permissions).
cmdr::validate::common - Consolidated multiple copies of "OkDir" in cmdr::validate into a single shared helper command "ok-directory".
cmdr::validate - Replaced all uses of "OkDir" with the shared "ok-directory". Changed the "rw*" types to allow missing file/dir/path like the "w*" types.. Fixed the fail messages for "wfile" and "wchan".
Merged trunk extensions.
Merged branch back, making the channel v-types official.