test-cache-abuse: correct for different hunk headers between Solaris and GNU

When diffing against an empty file, Solaris diff uses 1 to designate the
first line of the empty file (either -1,0 on the left or +1,0 on the right)
while GNU diff uses 0 (-0,0 and +0,0).  We use a glob here to make sure the
test passes with either toolchain.

I've not added tests to check-code because there are scads of places in the
tests where the GNU format is used due to that being the format that "hg
diff" and "hg export" use, and changing those to use globs seems wrong.

tests/test-cache-abuse.t

@@ -88,7 +88,7 We currently can't detect an rbc cache w
   $ damage "log -qr branch(b2)" rbc-names-v1
   --- before	* (glob)
   +++ after	* (glob)
-  @@ -1,8 +0,0 @@
+  @@ -1,8 +?,0 @@ (glob)
   -2:5fb7d38b9dc4
   -3:60b597ffdafa
   -4:b1174d11b69e