Numerous fixes and enhancements

Import str_argv_cat() and resolve_hostname() from LPJS
Add numeric comparison functions for qsort(), etc.
Add xt_factorial(): Lookup table based factorial for n up to 20
Add xt_n_choose_k(n,k) to compute n choose k
Eliminate mutator macros. Functions can be inlined if speed is that
critical. Also simplifies install on case-insensitive filesystems
where UC and LC man pages conflict.
Numerous other minor enhancements and fixes