MFC r332557-r332558, r332560, r332565: loader command cleanup-lite

r332557:
loader: make sure we use snprintf() in commands.c

Safeguard against memory corruptions.

r332558:
loader: command_errmsg should be const

Use const char * for command_errmsg.

r332560:
loader: make sure we do not return garbage from help_getnext

Since we do free subtopic and desc in help_getnext(), we need to set them also
NULL, so we make sure we dont get double free().

r332565:
loader: cstyle cleanup of command.c

just clean it up. no functional changes intended.