maint: fix recent stale comments and spelling mistakes

* doc/coreutils.texi: s/seperator/separator/.
* tests/misc/env-S.pl: Likewise.
* src/env.c: Fix stale comment.

doc/coreutils.texi

@@ -17341,7 +17341,7 @@ This escape sequence works inside single-quoted strings.
 @end multitable
 
 The following @command{awk} script will use tab character as input and output
-field seperator (instead of spaces and tabs):
+field separator (instead of spaces and tabs):
 
 @example
 $ cat tabs.awk

src/env.c

@@ -566,7 +566,7 @@ main (int argc, char **argv)
           break;
         case ' ':
         case '\t':
-          /* Space,tab,dash are undocumented options. Attempt to detect
+          /* These are undocumented options. Attempt to detect
              incorrect shebang usage with extraneous space, e.g.:
                 #!/usr/bin/env -i command
              In which case argv[1] == "-i command".  */

tests/misc/env-S.pl

@@ -139,7 +139,7 @@ my @Tests =
      ['d11', q[-S'echo FOO \\#BAR'],    {OUT=>"FOO #BAR"}],
      ['d12', q[-S'echo FOO#BAR'],       {OUT=>"FOO#BAR"}],
 
-     # Test underscore as space/seperator in double/single/no quotes
+     # Test underscore as space/separator in double/single/no quotes
      ['s1',  q[-S'printf x%sx\\n "A\\_B"'],   {OUT=>"xA Bx"}],
      ['s2',  q[-S"printf x%sx\\n 'A\\_B'"],   {OUT=>"xA\\_Bx"}],
      ['s3',  q[-S"printf x%sx\\n A\\_B"],     {OUT=>"xAx\nxBx"}],