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/sh/parse.c

@@ -172,9 +172,7 @@ static void typeset_order(const char *str,int line)
 		return;
 	if(!table)
 	{
-		table = calloc(1,256);
-		if(!table)
-			sh_outofmemory();
+		table = sh_calloc(1,256);
 		for(cp=(unsigned char*)"bflmnprstuxACHS";c = *cp; cp++)
 			table[c] = 1;
 		for(cp=(unsigned char*)"aiEFLRXhTZ";c = *cp; cp++)