Get USART 2 & 3 working on lpc4357-evb. These changes are required to get USART 2 and 3 working on the Embest development board.  From Toby Duckworth

Remove CONFIG_DEBUG_STACK.  Adding CONFIG_STACK_COLORATION makes this configuration option pointless

Add CONFIG_STACK_COLORATION that does the same thing as CONFIG_DEBUG_STACK but without enabling debug.  From David Sidrane

Math library: Adds support for the expm1 functions: http://pubs.opengroup.org/onlinepubs/009695399/functions/expm1.html.  From Brennan Ashton

Networking:  IPv4 and IPv6 work together.  This fixes a bug necessary to accomplish that as well as cleaning up a couple of other issues

apps/nshlib:  Add the ping6 command to support checking IPv6 networks.  NSH logic is complete but still missing some network level support

Armv7-M: Remove Px4-only setting of stack to 0xff.  This is incompatible with standard NuttX stack montitoring logic

Armv7-M: Remove Px4-only setting of stack to 0xff.  This is incompatible with standard NuttX stack montitoring logic

Networking:  New domain field in socket structure is created by socket(), but missed cases where a socket is created via accept() or dup()