LICENSE: Add Threadpool license text.

LICENSE

@@ -4,6 +4,8 @@ Log4cplus license
 Each file of log4cplus source is licensed using either two clause BSD
 license or Apache license 2.0. Log4cplus is derived work from log4j.
 
+Threadpool code is licensed under separate license.
+
 
 Two clause BSD license
 ----------------------
@@ -420,3 +422,31 @@ archives.
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
+
+
+Threadpool license
+==================
+
+Copyright (c) 2012-2015 Jakob Progsch
+
+This software is provided 'as-is', without any express or implied
+warranty. In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+   1. The origin of this software must not be misrepresented; you must not
+   claim that you wrote the original software. If you use this software
+   in a product, an acknowledgment in the product documentation would be
+   appreciated but is not required.
+
+   2. Altered source versions must be plainly marked as such, and must not be
+   misrepresented as being the original software.
+
+   3. This notice may not be removed or altered from any source
+   distribution.
+
+Modified for log4cplus, copyright (c) 2014-2015 Václav Zeman.
+