The NSH shutdown option should be called --reboot, not --reset, for compatibility with the statndard shutdown command

system/poweroff:  Use prototype for board_power_off() from include/nuttx/board.h, not from non-supported power.h header file

Fix references to the no-longer-existent misc/ directory in comments, README files, and documentation

THTTPD: Remove use of lstat when directory indexing is enabled.  NuttX does not support symbolic links

Fix a few errors/warnings in THTTPD when indexing is enabled.  Still depends on non-existent lstat and ctime