Add more out of memory checks (re: 18529b88) (#192)

The referenced commit neglected to add checks for strdup() calls.
That calls malloc() as well, and is used a lot.

This commit switches to another strategy: it adds wrapper functions
for all the allocation macros that check if the allocation
succeeded, so those checks don't need to be done manually.

src/cmd/ksh93/include/defs.h,
src/cmd/ksh93/sh/init.c:
- Add sh_malloc(), sh_realloc(), sh_calloc(), sh_strdup(),
  sh_memdup() wrapper functions with success checks. Call nospace()
  to error out if allocation fails.
- Update new_of() macro to use sh_malloc().
- Define new sh_newof() macro to replace newof(); it uses
  sh_realloc().

All other changed files:
- Replace the relevant calls with the wrappers.
- Remove now-redundant success checks from 18529b88.
- The ERROR_PANIC error message calls are updated to inclusive-or
  ERROR_SYSTEM into the exit code argument, so libast's error()
  appends the human-readable version of errno in square brackets.
  See src/lib/libast/man/error.3

src/cmd/ksh93/edit/history.c:
- Include "defs.h" to get access to the wrappers even if KSHELL is
  not defined.
- Since we're here, fix a compile error that occurred with KSHELL
  undefined by updating the type definition of hist_fname[] to
  match that of history.h.

src/cmd/ksh93/bltins/enum.c:
- To get access to sh_newof(), include "defs.h" instead of
  <shell.h> (note that "defs.h" includes <shell.h> itself).

src/cmd/ksh93/Mamfile:
- enum.c: depend on defs.h instead of shell.h.
- enum.o: add an -I. flag in the compiler invocation so that defs.h
  can find its subsequent includes.

src/cmd/builtin/pty.c:
- Define one outofmemory() function and call that instead of
  repeating the error message call.
- outofmemory() never returns, so remove superfluous exit handling.

Co-authored-by: Martijn Dekker <martijn@inlv.org>

src/cmd/ksh93/bltins/enum.c

@@ -18,7 +18,7 @@
 *                                                                      *
 ***********************************************************************/
 #pragma prototyped
-#include	<shell.h>
+#include	"defs.h"
 
 static const char enum_usage[] =
 "[-?@(#)$Id: enum (AT&T Research) 2008-01-08 $\n]"
@@ -112,7 +112,7 @@ static int enuminfo(Opt_t* op, Sfio_t *out, const char *str, Optdisc_t *fp)
 static Namfun_t *clone_enum(Namval_t* np, Namval_t *mp, int flags, Namfun_t *fp)
 {
 	struct Enum	*ep, *pp=(struct Enum*)fp;
-	ep = newof(0,struct Enum,1,pp->nelem*sizeof(char*));
+	ep = sh_newof(0,struct Enum,1,pp->nelem*sizeof(char*));
 	memcpy((void*)ep,(void*)pp,sizeof(struct Enum)+pp->nelem*sizeof(char*));
 	return(&ep->hdr);
 }
@@ -228,8 +228,7 @@ int b_enum(int argc, char** argv, Shbltin_t *context)
 		}
 		while(nv_nextsub(np));
 		sz += n*sizeof(char*);
-		if(!(ep = newof(0,struct Enum,1,sz)))
-			error(ERROR_system(1), "out of space");
+		ep = sh_newof(0,struct Enum,1,sz);
 		ep->iflag = iflag;
 		ep->nelem = n;
 		cp = (char*)&ep->values[n+1];