rm redundant hardcoded default paths (re: aa4669ad)

As of aa4669ad, astconf("PATH") is implemented as a hardcoded AST
configuration variable that always has a value, instead of one that
falls back on the OS. Its value is now obtained from the OS (with a
fallback) at configure time and not at runtime. This means that any
fallback for astconf("PATH") is now never used.

src/cmd/ksh93/data/msg.c,
src/cmd/ksh93/include/shell.h:
- Remove e_defpath[]. (The path "/bin:/usr/bin:" made no sense as a
  default path anyway, as the final empty element is wrong: default
  utilities should never be sought in the current working dir.)

src/cmd/ksh93/sh/path.c,
src/lib/libast/path/pathbin.c:
- abort() if astconf("PATH") returns null.

src/lib/libast/comp/conf.tab: PATH:
- If no 'getconf' utility can be found, use a fallback path that
  finds more utilities by also searching in 'sbin' directories.
  On some systems, this is needed to find chown(1).

src/cmd/ksh93/sh.1:
- Update doc re default path.

src/cmd/ksh93/data/msg.c

@@ -170,7 +170,6 @@ const char e_heading[]		= "Current option settings";
 const char e_sptbnl[]		= " \t\n";
 const char e_tolower[]		= "tolower";
 const char e_toupper[]		= "toupper";
-const char e_defpath[]		= "/bin:/usr/bin:";
 const char e_defedit[]		= _pth_ed;
 const char e_unknown []		= "<command unknown>";
 const char e_devnull[]		= "/dev/null";

src/cmd/ksh93/include/shell.h

@@ -106,7 +106,6 @@ typedef union Shnode_u Shnode_t;
 /* The following type is used for error messages */
 
 /* error messages */
-extern const char	e_defpath[];
 extern const char	e_found[];
 extern const char	e_nospace[];
 extern const char	e_format[];

src/cmd/ksh93/sh.1

@@ -4189,15 +4189,9 @@ search for the command name.
 Alternative directory names are separated by
 a colon
 .RB ( : ).
-The default path is equal to the output of
+The default path is the value that was output by
-.BI builtin\ getconf;\ getconf\ PATH
+.BI getconf\ PATH
-or, if the OS doesn't provide that value,
+at the time ksh was compiled.
-.B /bin:/usr/bin:
-(specifying
-.BR /bin ,
-.BR /usr/bin ,
-and the current directory
-in that order).
 The current directory can be specified by
 two or more adjacent colons, or by a colon
 at the beginning or end of the path list.

src/cmd/ksh93/sh/path.c

@@ -454,7 +454,7 @@ Pathcomp_t *path_nextcomp(Shell_t *shp,register Pathcomp_t *pp, const char *name
 static Pathcomp_t* defpath_init(Shell_t *shp)
 {
 	if(!std_path && !(std_path=astconf("PATH",NIL(char*),NIL(char*))))
-		std_path = e_defpath;
+		abort();
 	Pathcomp_t *pp = (void*)path_addpath(shp,(Pathcomp_t*)0,(std_path),PATH_PATH);
 	return(pp);
 }

src/lib/libast/comp/conf.tab

@@ -375,7 +375,7 @@ PATH				AST	CS 1 MU		sh{
 	*)	CONF_path=`"$CONF_getconf" PATH` ;;
 	esac
 	case $CONF_path in
-	'')	echo '"/bin:/usr/bin"' ;;
+	'')	echo '"/bin:/usr/bin:/sbin:/usr/sbin"' ;;
 	*)	echo "\\"$CONF_path\\"" ;;
 	esac
 }

src/lib/libast/path/pathbin.c

@@ -39,7 +39,7 @@ pathbin(void)
 	if ((!(bin = getenv("PATH")) || !*bin) && !(bin = val))
 	{
 		if (!*(bin = astconf("PATH", NiL, NiL)) || !(bin = strdup(bin)))
-			bin = "/bin:/usr/bin:/usr/local/bin";
+			abort();
 		val = bin;
 	}
 	return bin;