Add external project include, google version numbers

Change-Id: I98336f7ecde8a774f9304abb639ff70a313cbe91

Author: wesm

CMakeLists.txt

@@ -13,10 +13,14 @@ project(pandas)
 
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake_modules")
 include(CMakeParseArguments)
+include(ExternalProject)
 
 set(BUILD_SUPPORT_DIR ${CMAKE_CURRENT_SOURCE_DIR}/build-support)
 set(THIRDPARTY_DIR ${CMAKE_CURRENT_SOURCE_DIR}/thirdparty)
 
+set(GTEST_VERSION "1.7.0")
+set(GBENCHMARK_VERSION "1.0.0")
+
 # Allow "make install" to not depend on all targets.
 #
 # Must be declared in the top-level CMakeLists.txt.