tests: add --keep-tmp to run-tests.py to debug test environment

When set, you can find the working dir of the test run as a
uniquely named subdirectory of --tmpdir so you can inspect
it.

tests/run-tests.py

@@ -38,6 +38,8 b' parser.add_option("-i", "--interactive",'
     help="prompt to accept changed output")
 parser.add_option("-j", "--jobs", type="int",
     help="number of jobs to run in parallel")
+parser.add_option("--keep-tmpdir", action="store_true",
+    help="keep temporary directory after running tests (best used with --tmpdir)")
 parser.add_option("-R", "--restart", action="store_true",
     help="restart at last error")
 parser.add_option("-p", "--port", type="int",
@@ -133,9 +135,10 b' def check_required_tools():'
             print "WARNING: Did not find prerequisite tool: "+p
 
 def cleanup_exit():
-    if verbose:
-        print "# Cleaning up HGTMP", HGTMP
-    shutil.rmtree(HGTMP, True)
+    if not options.keep_tmpdir:
+        if verbose:
+            print "# Cleaning up HGTMP", HGTMP
+        shutil.rmtree(HGTMP, True)
 
 def use_correct_python():
     # some tests run python interpreter. they must use same
@@ -398,7 +401,8 b' def run_one(test, skips):'
         pass
 
     os.chdir(TESTDIR)
-    shutil.rmtree(tmpd, True)
+    if not options.keep_tmpdir:
+	    shutil.rmtree(tmpd, True)
     if skipped:
         return None
     return ret == 0