tests: add -k to test scripts matching keywords

argument is a space-separated list of keywords that are searched for
in the name and body of each test. This makes it easy to run only
tests related to tags, hgweb, revert, etc. (eg -k "tag hgweb revert").

tests/run-tests.py

@@ -90,6 +90,8 b' def parseargs():'
     parser.add_option("-j", "--jobs", type="int",
         help="number of jobs to run in parallel"
              " (default: $%s or %d)" % defaults['jobs'])
+    parser.add_option("-k", "--keywords",
+        help="run tests matching keywords")
     parser.add_option("--keep-tmpdir", action="store_true",
         help="keep temporary directory after running tests"
              " (best used with --tmpdir)")
@@ -688,10 +690,21 b' def runtests(options, tests):'
 
         skips = []
         fails = []
+
         for test in tests:
             if options.retest and not os.path.exists(test + ".err"):
                 skipped += 1
                 continue
+
+            if options.keywords:
+                t = open(test).read().lower() + test.lower()
+                for k in options.keywords.lower().split():
+                    if k in t:
+                        break
+                else:
+                    skipped +=1
+                    continue
+
             ret = runone(options, test, skips, fails)
             if ret is None:
                 skipped += 1