Lots of man page fixes and some other minor fixes (#284)

Noteworthy changes:
- The man pages have been updated to fix a ton of instances of
  runaway underlining (this was done with `sed -i 's/\\f5/\\f3/g'`
  commands). This commit dramatically increased in size because
  of this change.
- The documentation for spawnveg(3) has been extended with
  information about its usage of posix_spawn(3) and vfork(2).
- The documentation for tmfmt(3) has been updated with the changes
  previously made to the man pages for the printf and date builtins
  (though the latter builtin is disabled by default).
- The shell's tracked alias tree (hash table) is now documented in
  the shell(3) man page.
- Removed the commented out regression test for an ERRNO variable
  as the COMPATIBILITY file states it was removed in ksh93.

src/cmd/ksh93/tests/variables.sh

@@ -44,14 +44,6 @@ set abc def
 if	[[ $_ != def ]]
 then	err_exit _ variable not working
 fi
-# ERRNO
-#set abc def
-#rm -f foobar#
-#ERRNO=
-#2> /dev/null < foobar#
-#if	(( ERRNO == 0 ))
-#then	err_exit ERRNO variable not working
-#fi
 # PWD
 if	[[ !  $PWD -ef . ]]
 then	err_exit PWD variable failed, not equivalent to .