Add script for setting files to git last touched date.

This may help with whatever issue is causing a problem with RISC OS
!Boot and !System distributions.

From the base of the netsurf repo, you can run it like this:

  $ ./utils/git-date.sh riscos/distribution/

utils/git-date.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+#
+# Copyright © 2016 Michael Drake <tlsa@netsurf-browser.org>
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+#   * The above copyright notice and this permission notice shall be included in
+#     all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+# Sets the timestamp of files to the last time a commit touched them in
+# the given subtree.
+#
+# Usage: git-date.sh <PATH>
+#
+# Example: /utils/git-date.sh riscos/distribution
+
+set -e
+
+for FILE in $(git ls-files ${1})
+do
+    TIME=$(git log --pretty=format:%cd -n 1 --date=iso "$FILE")
+    touch -m -d "$TIME" "$FILE"
+done