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.

NEWS

@@ -10,6 +10,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
   that 'unalias -a' does not remove them. Shell functions can now use
   these names, which improves compatibility with POSIX shell scripts.
 
+- The two default aliases that are left, 'history' and 'r', are now only
+  loaded on interactive shells, leaving zero default aliases for scripts.
+
 - The End key escape sequence '^[[F' is now handled in the emacs and vi editing
   modes. The End key moves the cursor to the end of the line (in contrast to
   the Home key doing the opposite).