Some safety fixes

[sleepybishop]

Hello, I ran into a few safety snags while interating norm into a project. Hopefully these are helpful.

• Replaced manual string bounds tracking and concatenation (strncpy, strncat, sprintf) with
  safe snprintf calls in normApi.cpp and normApp.cpp. This prevents potential buffer overflows and ensures path lengths safely respect PATH_MAX.
• Added a missing lower-bound validation check in normMessage.cpp to verify that header_length is at least
  header_length_base before proceeding. This prevents out-of-bounds memory reads on malformed packets.
• Updated a deprecated waf API call (ctx.parser.add_argument_group to ctx.add_option_group) in wscript for
  compatibility with modern waf versions.