sort: make GNU test sort-debug-keys pass (#2269)

* sort: disable support for thousand separators

In order to be compatible with GNU, we have to disable thousands
separators. GNU does not enable them for the C locale, either.

Once we add support for locales we can add this feature back.

* sort: delete unused fixtures

* sort: compare -0 and 0 equal

I must have misunderstood this when implementing, but GNU considers
-0, 0, and invalid numbers to be equal.

* sort: strip blanks before applying the char index

* sort: don't crash when key start is after key end

* sort: add "no match" for months at the first non-whitespace char

We should put the "^ no match for key" indicator at the first
non-whitespace character of a field.

* sort: improve support for e notation

* sort: use maches! macros

tests/by-util/test_sort.rs

@@ -526,6 +526,11 @@ fn test_keys_with_options_blanks_start() {
     }
 }
 
+#[test]
+fn test_keys_blanks_with_char_idx() {
+    test_helper("keys_blanks", &["-k 1.2b"])
+}
+
 #[test]
 fn test_keys_with_options_blanks_end() {
     let input = "a  b
@@ -574,6 +579,13 @@ aaaa
         .stdout_only(input);
 }
 
+#[test]
+fn test_keys_negative_size_match() {
+    // If the end of a field is before its start, we should not crash.
+    // Debug output should report "no match for key" at the start position (i.e. the later position).
+    test_helper("keys_negative_size", &["-k 3,1"]);
+}
+
 #[test]
 fn test_zero_terminated() {
     test_helper("zero-terminated", &["-z"]);