* Changed configure.in to use gcc -Wall even without --enable-debug, to prevent

* Changed configure.in to use gcc -Wall even without --enable-debug, to prevent
  developers compiling optimized from introducing warnings, and to give
  end-users a warm, fuzzy feeling as they (hopefully) see no warnings come out
  (except perhaps on the lex output file) even with -Wall.

* Renamed getpass() to nmh_getpass() since the prototype for getpass() varies
  from OS to OS, and we want to _always_ use our version of the function.  Fixed
  all the callers to use nmh_getpass() and added it to prototypes.h.
  Semi-arbitrarily upped MAX_PASSWORD_LEN from 128 to 256.  buf was being
  calloc()'d and the memory leaked -- should have just been declared as static
  char array.  Prepended "Portions of this code are" to the copyright message,
  as this version has been changed significantly from the BSD version.

* Added "nmh-local functions to use in preference to OS versions" section to
  README.developers (currently just says to use nmh_getpass() instead of system
  getpass()).