Load 'r' and 'history' default aliases on interactive only

These two default aliases are useful on interactive shells. In
scripts, they interfere with possible function or command names.

As of this commit, these final two default aliases are only loaded
for interactive shells, leaving zero default aliases for scripts.
This completes the project to get rid of misguided default aliases.

src/cmd/ksh93/include/shtable.h,
src/cmd/ksh93/data/aliases.c:
src/cmd/ksh93/sh/init.c:
- Add empty alias table shtab_noaliases[] for scripts.
- Rename inittree() to sh_inittree() and make it external.
- nv_init(), sh_reinit(): Initialise empty alias tree for scripts.

src/cmd/ksh93/sh/main.c: sh_main():
- If interactive, reinitialise alias tree for interactive shells.

src/cmd/ksh93/tests/alias.sh:
- To test default alias removal, launch shell with -i.

TODO

@@ -14,27 +14,6 @@ Fix build system:
   to take effect. The machine-generated Mamfiles are now used as a fallback,
   but they are not meant to be edited by hand.
 
-______
-Fix or remove broken or misguided default aliases:
-
-- Make proper builtins out of the following scripting-related aliases, so
-  that 'unalias -a' does not eliminate them. If done correctly, this causes
-  no other change in behaviour. It would be good practice to 'unalias -a' in
-  a script to start with a clean slate, except ksh has always made that
-  impossible without losing these. Default aliases should be to facilitate
-  interactive use.
-	- autoload='typeset -fu'
-	- compound='typeset -C'
-	- float='typeset -lE'
-	- functions='typeset -f'
-	- integer='typeset -li'
-	- nameref='typeset -n'
-  Keep these default aliases for the benefit of interactive shells:
-	+ history='hist -l'
-	+ r='hist -s'
-  To avoid interfering with shell functions by those names that POSIX
-  scripts may set, those should only initialise on interactive shells.
-
 ______
 Fix currently known bugs affecting shell scripting. These are identified by
 their modernish IDs. For exact details, see code/comments in: