sort: fix -kN,M handling (was including last separator into the comparison)

Testcase:

$ printf '%s\n' a/a:a a:b | sort -t: -k1,1
a:b
a/a:a

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/sort.c

@@ -25,14 +25,14 @@
 //usage:     "\n	-f	Ignore case"
 //usage:     "\n	-g	General numerical sort"
 //usage:     "\n	-i	Ignore unprintable characters"
-//usage:     "\n	-k	Sort key"
 //usage:     "\n	-M	Sort month"
 //usage:	)
+//-h, --human-numeric-sort: compare human readable numbers (e.g., 2K 1G)
 //usage:     "\n	-n	Sort numbers"
 //usage:	IF_FEATURE_SORT_BIG(
 //usage:     "\n	-o	Output to file"
-//usage:     "\n	-k	Sort by key"
-//usage:     "\n	-t CHAR	Key separator"
+//usage:     "\n	-t CHAR	Field separator"
+//usage:     "\n	-k N[,M] Sort by Nth field"
 //usage:	)
 //usage:     "\n	-r	Reverse sort order"
 //usage:	IF_FEATURE_SORT_BIG(
@@ -143,6 +143,9 @@ static char *get_key(char *str, struct sort_key *key, int flags)
 					}
 				}
 			}
+			/* Remove last delim: "abc:def:" => "abc:def" */
+			if (key_separator && j && end != 0)
+				end--;
 		}
 		if (!j) start = end;
 	}
@@ -163,7 +166,8 @@ static char *get_key(char *str, struct sort_key *key, int flags)
 		if (start > len) start = len;
 	}
 	/* Make the copy */
-	if (end < start) end = start;
+	if (end < start)
+		end = start;
 	str = xstrndup(str+start, end-start);
 	/* Handle -d */
 	if (flags & FLAG_d) {

testsuite/sort.tests

@@ -98,6 +98,14 @@ testing "sort with non-default leading delim 3" "sort -n -k3 -t/ input" "\
 //b/1
 " ""
 
+testing "sort with non-default leading delim 4" "sort -t: -k1,1 input" "\
+a:b
+a/a:a
+" "\
+a/a:a
+a:b
+" ""
+
 testing "sort -u should consider field only when discarding" "sort -u -k2 input" "\
 a c
 " "\