Several Makefiles: Add .PHONY definitions to prevent 'clean up to date' message weirdness; Add default definitions for some commonly used things when 'make clean' is used without .config or Make.defs files installed.

Add a simple test of the scheduler instrumentation logic.  This initial version is still kind of buggy.

apps/modbus/nuttx/portserial.c:  Was not returning an error on failure to open the device driver.  From Olololshka kokoko

DHCPD no longer calls directly into the OS, but uses network IOCTL commands to modify the ARP table.

Low level drive access functions should not generate output; it interferes with higher level formatting

apps/platform/Makefile:  Use a relative path to the board directory link rather than the absolute path.  For Cygwin, the absolute would would need converted with cygpath.  But just using the relative path is a simpler solution.

system/ramtron is now EXPERIMENTAL because it violates the OS interface boundard by calling up_spiinitialize() directly.  The function up_spiinitialize has been obsoleted and is no longer available

NSH: Add option to use platform-specific logic to verify login credentials; Add option to add a delay after each failed login attempt

apps/nshlib:  All NSH sessions may now be protected with passwords stored in the encrypted /etc/passwd file