Enable CurlClient tests on Windows by bundling curl.exe.

third_party/curl/curl.LICENSE

Index: third_party/curl/curl.LICENSE
diff --git a/third_party/curl/curl.LICENSE b/third_party/curl/curl.LICENSE
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index 0000000000000000000000000000000000000000..18f1684b137b7ae93b1b5e70befe00fe18eb3115
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+++ b/third_party/curl/curl.LICENSE
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+COPYRIGHT AND PERMISSION NOTICE
+
+Copyright (c) 1996 - 2012, Daniel Stenberg, <daniel@haxx.se>.
+
+All rights reserved.
+
+Permission to use, copy, modify, and 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", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS. 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.
+
+Except as contained in this notice, the name of a copyright holder shall not
+be used in advertising or otherwise to promote the sale, use or other dealings
+in this Software without prior written authorization of the copyright holder.