Attempt #2 to fix that FPATH crash (re: 6ffab55)

The name.c change in that commit was ineffective at fixing the
crash; I was misled by the crash being intermittent. The same crash
in path_unsetfpath() continues to occur sometimes when FPATH is set
in bin/package.

This commit special-cases FPATH in sh_reinit(), which is used to
(partially) reinitialise the shell after forking and before running
a shell script without a hashbang path. It is a bit of a hack, but
then again the entire sh_reinit() thing is a hack that I plan to
get rid of eventually; for now, it just needs to not crash.

src/cmd/ksh93/sh/name.c: sh_envnolocal():
- Revert the ineffective fix.

src/cmd/ksh93/sh/init.c: sh_reinit():
- Before starting reinit, save FPATH's value if it has the export
  attribute, then unset FPATH.
- After reinit is done, restore FPATH's value and export attribute
  if the value was saved. This should reinitialise sh.fpathdict.

Fingers crossed...

src/cmd/ksh93/sh/init.c

@@ -1513,6 +1513,7 @@ int sh_reinit(char *argv[])
 	Namval_t *np,*npnext;
 	Dt_t	*dp;
 	int	nofree;
+	char	*savfpath = NULL;
 	sh_onstate(SH_INIT);
 	sh.subshell = sh.realsubshell = sh.comsub = sh.curenv = sh.jobenv = sh.inuse_bits = sh.fn_depth = sh.dot_depth = 0;
 	sh.envlist = NULL;
@@ -1522,6 +1523,10 @@ int sh_reinit(char *argv[])
 		sfclose(sh.heredocs);
 		sh.heredocs = 0;
 	}
+	/* save FPATH and treat specially */
+	if(nv_isattr(FPATHNOD,NV_EXPORT))
+		savfpath = sh_strdup(nv_getval(FPATHNOD));
+	_nv_unset(FPATHNOD,NV_RDONLY);
 	/* Remove non-exported variables, first pass (see sh_envnolocal() in name.c) */
 	nv_scan(sh.var_tree,sh_envnolocal,NULL,NV_EXPORT,0);
 	nv_scan(sh.var_tree,sh_envnolocal,NULL,NV_ARRAY,NV_ARRAY);
@@ -1665,6 +1670,13 @@ int sh_reinit(char *argv[])
 	/* update $$, $PPID */
 	sh.ppid = sh.current_ppid;
 	sh.pid = sh.current_pid;
+	/* restore an exported FPATH */
+	if(savfpath)
+	{
+		nv_setattr(FPATHNOD,NV_EXPORT);
+		nv_putval(FPATHNOD,savfpath,0);
+		free(savfpath);
+	}
 	/* call user init function, if any */
 	if(sh.userinit)
 		(*sh.userinit)(&sh, 1);

src/cmd/ksh93/sh/name.c

@@ -2282,8 +2282,6 @@ void	sh_envnolocal (Namval_t *np, void *data)
 		return;
 	if(np==L_ARGNOD)
 		return;
-	if(np==FPATHNOD)
-		return;
 	if(np == sh.namespace)
 		return;
 	if(nv_isref(np))