tests: factor external procedures out for portability

Fortunately, "&&" is treated as "execute next, if previous doesn't
fail" both on POSIX and Windows. But keeping portability of
"dirstaterace.command" manually is troublesome.

This patch factors external procedures out as a shell script for
portability. "sh SCRIPT" always allows scripting in POSIX style.

This change is also for convenience. Fixed script name can reduce
command line arguments.

"r" prefix is needed for "sh '$TESTTMP/dirstaterace.sh'", because
$TESTTMP contains backslash on Windows.

tests/test-dirstate-race.t

@@ -1,93 +1,97
   $ hg init repo
   $ cd repo
   $ echo a > a
   $ hg add a
   $ hg commit -m test
 
 Do we ever miss a sub-second change?:
 
   $ for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20; do
   >     hg co -qC 0
   >     echo b > a
   >     hg st
   > done
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
   M a
 
   $ echo test > b
   $ mkdir dir1
   $ echo test > dir1/c
   $ echo test > d
 
   $ echo test > e
 #if execbit
 A directory will typically have the execute bit -- make sure it doesn't get
 confused with a file with the exec bit set
   $ chmod +x e
 #endif
 
   $ hg add b dir1 d e
   adding dir1/c (glob)
   $ hg commit -m test2
 
   $ cat >> $TESTTMP/dirstaterace.py << EOF
   > from mercurial import (
   >     context,
   >     extensions,
   > )
   > def extsetup():
   >     extensions.wrapfunction(context.workingctx, '_checklookup', overridechecklookup)
   > def overridechecklookup(orig, self, files):
   >     # make an update that changes the dirstate from underneath
-  >     self._repo.ui.system(self._repo.ui.config('dirstaterace', 'command'), cwd=self._repo.root)
+  >     self._repo.ui.system(r"sh '$TESTTMP/dirstaterace.sh'",
+  >                          cwd=self._repo.root)
   >     return orig(self, files)
   > EOF
 
   $ hg debugrebuilddirstate
   $ hg debugdirstate
   n   0         -1 unset               a
   n   0         -1 unset               b
   n   0         -1 unset               d
   n   0         -1 unset               dir1/c
   n   0         -1 unset               e
 
 XXX Note that this returns M for files that got replaced by directories. This is
 definitely a bug, but the fix for that is hard and the next status run is fine
 anyway.
 
-  $ hg status --config extensions.dirstaterace=$TESTTMP/dirstaterace.py \
-  >   --config dirstaterace.command='rm b && rm -r dir1 && rm d && mkdir d && rm e && mkdir e'
+  $ cat > $TESTTMP/dirstaterace.sh <<EOF
+  > rm b && rm -r dir1 && rm d && mkdir d && rm e && mkdir e
+  > EOF
+
+  $ hg status --config extensions.dirstaterace=$TESTTMP/dirstaterace.py
   M d
   M e
   ! b
   ! dir1/c
   $ hg debugdirstate
   n 644          2 * a (glob)
   n   0         -1 unset               b
   n   0         -1 unset               d
   n   0         -1 unset               dir1/c
   n   0         -1 unset               e
 
   $ hg status
   ! b
   ! d
   ! dir1/c
   ! e