test/[: binary operators: fix '<' and add '=~'; some more cleanups

In ksh88, the test/[ built-in supported both the '<' and '>'
lexical sorting comparison operators, same as in [[. However, in
every version of ksh93, '<' does not work though '>' still does!

Still, the code for both is present in test_binop():

src/cmd/ksh93/bltins/test.c
548:		case TEST_SGT:
549:			return(strcoll(left, right)>0);
550:		case TEST_SLT:
551:			return(strcoll(left, right)<0);

Analysis: The binary operators are looked up in shtab_testops[] in
data/testops.c using a macro called sh_lookup, which expands to a
sh_locate() call. If we examine that function in sh/string.c, it's
easy to see that on systems using ASCII (i.e. all except IBM
mainframes), it assumes the table is sorted in ASCII order.

src/cmd/ksh93/sh/string.c
64:	while((c= *tp->sh_name) && (CC_NATIVE!=CC_ASCII || c <= first))

The problem was that the '<' operator was not correctly sorted in
shtab_testops[]; it was sorted immediately before '>', but after
'='. The ASCII order is: < (60), = (61), > (62). This caused '<' to
never be found in the table.

The test_binop() function is also used by [[, yet '<' always worked
in that. This is because the parser has code that directly checks
for '<' and '>' within [[ (in sh/parse.c, lines 1949-1952).

This commit also adds '=~' to 'test', which took three lines of
code and allowed eliminating error handling in test_binop() as
test/[ and [[ now support the same binary ops. (re: fc2d5a60)

src/cmd/ksh93/*/*.[ch]:
- Rename a couple of very misleadingly named macros in test.h:
  . For == and !=, the TEST_PATTERN bit is off for pattern compares
    and on for literal string compares! Rename to TEST_STRCMP.
  . The TEST_BINOP bit does not denote all binary operators, but
    only the logical -a/-o ops in test/[. Rename to TEST_ANDOR.

src/cmd/ksh93/bltins/test.c: test_binop():
- Add support for =~. This is only used by test/[. The method is
  implemented in two lines that convert the ERE to a shell pattern
  by prefixing it with ~(E), then call test_strmatch with that
  temporary string to match the ERE and update ${.sh.match}.
- Since all binary ops from shtab_testops[] are now accounted for,
  remove unknown op error handling from this function.

src/cmd/ksh93/data/testops.c:
- shtab_testops[]:
  . Correctly sort the '<' (TEST_SLT) entry.
  . Remove ']]' (TEST_END). It's not an op and doesn't belong here.
- Update sh_opttest[] documentation with =~, \<, \>.
- Remove now-unused e_unsupported_op[] error message.

src/cmd/ksh93/sh/lex.c: sh_lex():
- Check for ']]' directly instead of relying on the removed
  TEST_END entry from shtab_testops[].

src/cmd/ksh93/tests/bracket.sh:
- Add relevant tests.

src/cmd/ksh93/tests/builtins.sh:
- Fix an old test that globally deleted the 'test' builtin. Delete
  it within the command substitution subshell only.
- Remove the test for non-support of =~ in test/[.
- Update the test for invalid test/[ op to use test directly.

src/cmd/ksh93/data/testops.c

@@ -31,6 +31,7 @@
 
 /*
  * This is the list of binary test and [[ ... ]] operators
+ * It must be sorted in ascending ASCII order
  */
 
 const Shtable_t shtab_testops[] =
@@ -47,12 +48,11 @@ const Shtable_t shtab_testops[] =
 		"-nt",		TEST_NT,
 		"-o",		TEST_OR,
 		"-ot",		TEST_OT,
+		"<",		TEST_SLT,
 		"=",		TEST_SEQ,
 		"==",		TEST_SEQ,
 		"=~",           TEST_REP,
-		"<",		TEST_SLT,
 		">",		TEST_SGT,
-		"]]",		TEST_END,
 		"",		0
 };
 
@@ -134,6 +134,9 @@ const char sh_opttest[] =
 	"[+\astring1\a = \astring2\a?\astring1\a is equal to \astring2\a.]"
 	"[+\astring1\a == \astring2\a *?Same as \b=\b.]"
 	"[+\astring1\a != \astring2\a?\astring1\a is not equal to \astring2\a.]"
+	"[+\astring1\a =~ \aere\a *?\astring1\a matches the extended regular expression \aere\a.]"
+	"[+\astring1\a \\< \astring2\a *?\astring1\a lexically sorts before \astring2\a.]"
+	"[+\astring1\a \\> \astring2\a *?\astring1\a lexically sorts after \astring2\a.]"
 	"[+\anum1\a -eq \anum2\a?\anum1\a is numerically equal to \anum2\a.]"
 	"[+\anum1\a -ne \anum2\a?\anum1\a is not numerically equal to \anum2\a.]"
 	"[+\anum1\a -lt \anum2\a?\anum1\a is less than \anum2\a.]"
@@ -167,6 +170,5 @@ const char test_opchars[]	= "HLNRSVOGCaeohrwxdcbfugkv"
 const char e_argument[]		= "argument expected";
 const char e_missing[]		= "%s missing";
 const char e_badop[]		= "%s: unknown operator";
-const char e_unsupported_op[]	= "%s: operator not supported; use [[ ... ]]";
 const char e_tstbegin[]		= "[[ ! ";
 const char e_tstend[]		= " ]]\n";