rebaseline.py: in option names, replace underscores with hyphens

Split off of already-reviewed https://codereview.chromium.org/15789010/ ('rebaseline.py: --tests and --configs are now FILTERS within json results')

Review URL: https://codereview.chromium.org/15904018

git-svn-id: http://skia.googlecode.com/svn/trunk@9504 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/rebaseline.py b/tools/rebaseline.py
index 2b84ff7..5d8ff7a 100755
--- a/tools/rebaseline.py
+++ b/tools/rebaseline.py
@@ -259,15 +259,15 @@
                     '"--configs 565 8888"; if unspecified, run a default ' +
                     'set of configs. This should ONLY be specified if ' +
                     '--tests has also been specified.')
-parser.add_argument('--dry_run', action='store_true',
+parser.add_argument('--dry-run', action='store_true',
                     help='instead of actually downloading files or adding ' +
                     'files to checkout, display a list of operations that ' +
                     'we would normally perform')
-parser.add_argument('--json_base_url',
+parser.add_argument('--json-base-url',
                     help='base URL from which to read JSON_FILENAME ' +
                     'files; defaults to %(default)s',
                     default='http://skia-autogen.googlecode.com/svn/gm-actual')
-parser.add_argument('--json_filename',
+parser.add_argument('--json-filename',
                     help='filename (under JSON_BASE_URL) to read a summary ' +
                     'of results from; defaults to %(default)s',
                     default='actual-results.json')