Fix type names starting with lowercase 'a' (#69)

Type names that start with a lowercase 'a' cause an error when used:

$ typeset -T al=(typeset bar)
$ al foo=(bar=testset)
/usr/bin/ksh: al: : invalid variable name

The error occurs because when the parser checks for the alias
builtin (to set 'assignment' to two instead of one), only the first
letter of 'argp->argval' is checked (rather than the entire
string). This was fixed in ksh93v- by comparing argp->argval
against "alias", but in ksh93u+m the check can simply be removed
because it is only run when a builtin has the BLT_DCL flag. As of
04b9171, the alias builtin does not have that flag.

src/cmd/ksh93/sh/parse.c:
- Remove the bugged check for the alias builtin.

src/cmd/ksh93/tests/types.sh:
- Add a regression test for type names starting with a lowercase 'a'.

src/cmd/ksh93/sh/parse.c

@@ -1477,7 +1477,7 @@ static Shnode_t *simple(Lex_t *lexp,int flag, struct ionod *io)
 						t->comnamp = (void*)np;
 					if(nv_isattr(np,BLT_DCL))
 					{
-						assignment = 1+(*argp->argval=='a');
+						assignment = 1;
 						if(np==SYSTYPESET)
 							lexp->intypeset = 1;
 						key_on = 1;