Removed the _fmode variable from the iob module to prevent dragging
in iob and other stream I/O functions to every program which uses the
low level handle-based I/O. Modified the binmode module to just supply
the _fmode definition and dispensed with the initializer. Moved both
old binmode and new txtmode module to handleio where they logically
belong (more than to the startup project).

[git-p4: depot-paths = "//depot/openwatcom/": change = 37543]