line-range: teach -L^:RE to search from start of file

The -L:RE option of blame/log searches from the end of the previous -L
range, if any. Add new notation -L^:RE to override this behavior and
search from start of file.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index 8ba2d51..7369d3c 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -48,6 +48,7 @@
 canned_test "-M -L ':f:b.c' parallel-change" parallel-change-f-to-main
 
 canned_test "-L 4,12:a.c -L :main:a.c simple" multiple
+canned_test "-L 4,18:a.c -L ^:main:a.c simple" multiple-overlapping
 canned_test "-L :main:a.c -L 4,18:a.c simple" multiple-overlapping
 canned_test "-L 4:a.c -L 8,12:a.c simple" multiple-superset
 canned_test "-L 8,12:a.c -L 4:a.c simple" multiple-superset