tools: add license boilerplate to check-imports.sh

Per: https://github.com/joyent/node/pull/6962

This applies only the first commit from https://github.com/joyent/node/pull/6962.

/cc @bnoorduis

Reviewed By: Ben Noordhuis <ben@strongloop.com>
PR-URL: https://github.com/nodejs/node/pull/2386

tools/check-imports.sh

@@ -1,5 +1,19 @@
 #!/bin/sh
 
+# Copyright (c) 2013, 2014, Ben Noordhuis <info@bnoordhuis.nl>
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
 SED=sed
 UNAME=`uname`