test-patch-offset: Don't use unified diff

Solaris diff -u likes to be "helpful" and tell that "No differences encountered"

tests/test-patch-offset

@@ -1,67 +1,67
 #!/bin/sh
 
 cat > writepatterns.py <<EOF
 import sys
 
 path = sys.argv[1]
 patterns = sys.argv[2:]
 
 fp = file(path, 'wb')
 for pattern in patterns:
     count = int(pattern[0:-1])
     char = pattern[-1] + '\n'
     fp.write(char*count)
 fp.close()
 EOF
 
 echo % prepare repo
 hg init a
 cd a
 
 # These initial lines of Xs were not in the original file used to generate
 # the patch.  So all the patch hunks need to be applied to a constant offset
 # within this file.  If the offset isn't tracked then the hunks can be
 # applied to the wrong lines of this file.
 python ../writepatterns.py a 34X 10A 1B 10A 1C 10A 1B 10A 1D 10A 1B 10A 1E 10A 1B 10A
 hg commit -Am adda
 
 # This is a cleaner patch generated via diff
 # In this case it reproduces the problem when
 # the output of hg export does not
 echo % import patch
 hg import -v -m 'b' -d '2 0' - <<EOF
 --- a/a	2009-12-08 19:26:17.000000000 -0800
 +++ b/a	2009-12-08 19:26:17.000000000 -0800
 @@ -9,7 +9,7 @@
  A
  A
  B
 -A
 +a
  A
  A
  A
 @@ -53,7 +53,7 @@
  A
  A
  B
 -A
 +a
  A
  A
  A
 @@ -75,7 +75,7 @@
  A
  A
  B
 -A
 +a
  A
  A
  A
 EOF
 
 echo % compare imported changes against reference file
 python ../writepatterns.py aref 34X 10A 1B 1a 9A 1C 10A 1B 10A 1D 10A 1B 1a 9A 1E 10A 1B 1a 9A
-diff -u aref a
+diff aref a