apps/: Replace irqsave() with enter_critical_section(); replace irqrestore() with leave_critical_section()

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

Move xyz_cxxinitialize.c from nuttx/configs/abc/src to apps/platform/abc/ (where xyz is the processor family and abc is the board)

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