NSH:  Add a break command; if-then-else and looping behavior can not be configured out of the build for small systems that need minimal scripting capability

NSH:  Loosen up if-then-else-fi syntx so that a command can be on the same line as the 'then' and 'else' tokens.  This allows, as an example, 'if true; then echo true; else echo false; fi' which is much more bash-like

You can now specify or override the default board sub-directory.  This is only useful when CONFIG_ARCH_BOARD_CUSTOM is used and the default board sub-directory is not available

Fix all Cortex-M3/4 implementations of up_disable_irq().  They were doing nothing.  Thanks to Manuel Stühn for the tip.

FAT: Fix some root directory logic that was conditionally done only for FAT32.  Apparently this needs to be done for all FAT types.  From Tridge via Lorenz Meier

If write buffering is enabled, then it is necessary to release the write buffer resources (callback structure) when the socket is closed

Add support for the SO_LINGER socket option.  Based on logic from Jason Jiang.  Utestested on initial commit