nx::shell reform: Provide an alternative nx::shell impl (nx::shell2), used by all four shell scripts. nx::shell2 builds on Tcl's event loop, rather than while + update. This avoids blocking the Tk main window (update). In addition, nx::shell2 is closer to Tcl's native shells (e.g., no extra lines on enter, catches EOF).
Started refactoring scripted shell environment into a single, package location (nx::shell) to ease sharing between nxsh & friends, as well as to facilitate implementingNX/XOTcl shells in wrapped applications (tclkits)
