log -L: improve error message on malformed argument

The old message did not mention the :regex:file form.

To avoid overly long lines, split the message into two lines (in case
item->string is long, it will be the only part truncated in a narrow
terminal).

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index 0901b30..4451127 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -54,14 +54,14 @@
 canned_test "-L 8,12:a.c -L 4:a.c simple" multiple-superset
 
 test_bad_opts "-L" "switch.*requires a value"
-test_bad_opts "-L b.c" "argument.*not of the form"
-test_bad_opts "-L 1:" "argument.*not of the form"
+test_bad_opts "-L b.c" "argument not .start,end:file"
+test_bad_opts "-L 1:" "argument not .start,end:file"
 test_bad_opts "-L 1:nonexistent" "There is no path"
 test_bad_opts "-L 1:simple" "There is no path"
-test_bad_opts "-L '/foo:b.c'" "argument.*not of the form"
+test_bad_opts "-L '/foo:b.c'" "argument not .start,end:file"
 test_bad_opts "-L 1000:b.c" "has only.*lines"
 test_bad_opts "-L 1,1000:b.c" "has only.*lines"
-test_bad_opts "-L :b.c" "argument.*not of the form"
+test_bad_opts "-L :b.c" "argument not .start,end:file"
 test_bad_opts "-L :foo:b.c" "no match"
 
 test_expect_success '-L X (X == nlines)' '