Build 0.5 on Solaris 2.6

[Noel Hunt <noel@jpmorgan.com>]

The signal handlers in unix.c seem to be written in BSD-style using
`sigcontext' which is only available when you compile with /usr/ucb/cc
in Solaris (which compiles against the ucb compatibility includes and
libraries).

I rewrote this code for SVR4 sigaction-style handlers and for want of
anything better used #ifdef SVR4 around this code:

*** unix.c      Thu Feb 25 14:32:00 1999
--- /tmp/scsh-0.5.1/unix.c      Wed Apr  9 05:06:06 1997
***************
*** 117,130 ****
  
  static RETSIGTYPE
  when_keyboard_interrupt(sig, code, scp)
- #ifdef SVR4
-      int sig;
-      siginfo_t *code;
-      void *scp;
- #else
       int sig, code;
       struct sigcontext *scp;
- #endif
  {
    Spending_interruptsS |= (1 << INTERRUPT_KEYBOARD);
    /* The following might be necessary with signal(), but shouldn't be
--- 117,124 ----
***************
*** 135,148 ****
  
  static RETSIGTYPE
  when_alarm_interrupt(sig, code, scp)
- #ifdef SVR4
-      int sig;
-      siginfo_t *code;
-      void *scp;
- #else
       int sig, code;
       struct sigcontext *scp;
- #endif
  {
    Spending_interruptsS |= (1 << INTERRUPT_ALARM);
    return;
--- 129,136 ----
***************
*** 150,163 ****
  
  static RETSIGTYPE
  when_pipe_interrupt(sig, code, scp)
- #ifdef SVR4
-      int sig;
-      siginfo_t *code;
-      void *scp;
- #else
       int sig, code;
       struct sigcontext *scp;
- #endif
  {
    return;
  }
--- 138,145 ----
***************
*** 171,192 ****
  void
  sysdep_init()
  {
- #ifdef SVR4
-   keyboard_action.sa_sigaction = when_keyboard_interrupt;
-   keyboard_action.sa_flags = SA_SIGINFO;
- #else
    keyboard_action.sa_handler = when_keyboard_interrupt;
    keyboard_action.sa_flags = 0;
- #endif
    sigemptyset(&keyboard_action.sa_mask);
  
- #ifdef SVR4
-   alarm_action.sa_sigaction = when_alarm_interrupt;
-   alarm_action.sa_flags = SA_SIGINFO;
- #else
    alarm_action.sa_handler = when_alarm_interrupt;
    alarm_action.sa_flags = 0;
- #endif
    sigemptyset(&alarm_action.sa_mask);
  
    sigaction(SIGINT, &keyboard_action, NULL);
--- 153,164 ----