illumos gate

issues found by gcc 7 build:

    ed.c: In function 'commands':
    ed.c:581:5: error: this statement may fall through [-Werror=implicit-fallthrough=]
       c = 'e';
       ~~^~~~~
    ed.c:582:2: note: here
      case 'e':
      ^~~~
    ed.c:680:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
       listf++;
       ~~~~~^~
    ed.c:681:2: note: here
      case 'p':
      ^~~~
    ed.c:702:11: error: this statement may fall through [-Werror=implicit-fallthrough=]
       fchange = 0;
       ~~~~~~~~^~~
    ed.c:703:2: note: here
      case 'q':
      ^~~~
    ed.c:706:3: error: this statement may fall through [-Werror=implicit-fallthrough=]
       quit(sig);
       ^~~~~~~~~
    ed.c:708:2: note: here
      case 'r':
      ^~~~
    ed.c: In function 'fspec':
    ed.c:2854:9: error: this statement may fall through [-Werror=implicit-fallthrough=]
          if (*(fsp+1) == ':') {
             ^
    ed.c:2865:4: note: here
        case ' ': continue;
        ^~~~
    cc1: all warnings being treated as errors