Fix I/O redirection in -c script (Solaris patch 280-23332860)

This change is pulled from here:
https://github.com/oracle/solaris-userland/blob/master/components/ksh93/patches/280-23332860.patch

Info and reproducers:
https://github.com/att/ast/issues/36

In a -c script (like ksh -c 'commands'), the last command
misredirects standard output if an EXIT or ERR trap is set.
This appears to be a side effect of the optimisation that
runs the last command without forking.

This applies a patch by George Lijo that flags these specific
cases and disables the optimisation.

src/cmd/ksh93/include/defs.h,
src/cmd/ksh93/bltins/trap.c,
src/cmd/ksh93/sh/init.c,
src/cmd/ksh93/sh/main.c,
src/cmd/ksh93/sh/xec.c:
- Apply patch as above.

src/cmd/ksh93/tests/io.sh:
- Add the reproducers from the bug report as regression tests.

src/cmd/ksh93/include/defs.h

@@ -272,7 +272,10 @@ struct shared
 	Namfun_t	nvfun; \
 	char		*mathnodes; \
 	char		*bltin_dir; \
-	struct Regress_s*regress;
+	struct Regress_s*regress; \
+	char 		exittrap; \
+	char 		errtrap; \
+	char 		end_fn;
 
 #include	<shell.h>