Can't test "-l"

[fabiop]

Configuration Information [Automatically generated, do not change]:
Machine: i386
OS: Linux
Compiler: gcc
Compilation CFLAGS:   -DHAVE_VFPRINTF -DHAVE_UNISTD_H -DHAVE_STDLIB_H 
-DHAVE_LIMITS_H        -DHAVE_GETGROUPS -DHAVE_RESOURCE -DHAVE_SYS_PARAM 
-DVOID_SIGHANDLER -DHAVE_GETDTABLESIZE -DHAVE_BCOPY -DHAVE_GETPW_DECLS 
-DHAVE_GETHOSTNAME -DHAVE_WAIT_H         -DHAVE_DUP2 -DHAVE_STRERROR  
-DHAVE_DIRENT_H -DHAVE_STRING_H        -DHAVE_VARARGS_H -DHAVE_STRCHR  
-DHAVE_DEV_FD        -Di386 -DLinux -DSHELL -DHAVE_ALLOCA -DHAVE_ALLOCA_H       
-g
uname output: Linux linpel1.if.usp.br 2.2.5-15 #1 Mon Apr 19 23:00:46 EDT 1999 
i686 unknown

Bash Version: 1.14
Patch Level: 7

Description:
        [Detailed description of the problem, suggestion, or complaint.]

$ if [ "-l" != "-a" ] ; then echo "ok" ; fi
[: -a: binary operator expected                <----- ?

$ aa='-l'
$ if [ $aa != "-k" ] ; then echo "ok" ; fi
[: -k: binary operator expected                <----- ?

Repeat-By:
        [Describe the sequence of events that causes the problem
        to occur.]

Fix:
        [Description of how to fix the problem.  If you don't know a
        fix for the problem, don't include this section.]