tests: fix test-patch.t on pickier /bin/sh implementations stable

tests: fix test-patch.t on pickier /bin/sh implementations

This is a graft of 0b39edeff033 and f44306940c94 from default because
I'm tired of seeing the FreeBSD build be red on stable. See those
revisions for details on what's going on here.

--- a/tests/test-patch.t	Wed Jun 06 12:53:26 2018 -0700
+++ b/tests/test-patch.t	Sun May 20 23:05:18 2018 -0400
@@ -92,7 +92,12 @@
 
 Error exit (issue4746)
 
-  $ hg import ../c/p --config ui.patch='sh -c "exit 1"'
+  $ cat >> exit1.py <<EOF
+  > import sys
+  > sys.exit(1)
+  > EOF
+
+  $ hg import ../c/p --config ui.patch="\"$PYTHON\" \"`pwd`/exit1.py\""
   applying ../c/p
   abort: patch command failed: exited with status 1
   [255]