feature testing tweaks
feature testing tweaks

bin/modernish:
- test for FTL_DEVCLOBBR without forking a subshell
- remove duplicate FTL_NOPPID test
- thisshellhas(): AT&T ksh93 version: --bi= now deals properly with builtins
  that act like externals (with pathnames and all)
- builtin(): hardened against invalid arguments
- extern(): forgot to quote "$#"

modernish/modernish