Bump required Boost version to 1.56.0

scripts/cmake/ExternalProjectBoost.cmake

@@ -14,9 +14,9 @@ if(NOT Boost_INCLUDE_DIRS)
 		set(BOOST_INCLUDEDIR "$ENV{CMAKE_LIBRARY_SEARCH_PATH}/include/boost*")
 	endif()
 	if(OGS_LIB_BOOST STREQUAL "System")
-		find_package(Boost 1.46.0 REQUIRED)
+		find_package(Boost ${OGS_BOOST_VERSION} REQUIRED)
 	elseif(OGS_LIB_BOOST STREQUAL "Default")
-		find_package(Boost 1.46.0)
+		find_package(Boost ${OGS_BOOST_VERSION})
 	endif()
 	if(Boost_FOUND)
 		set(Boost_FOUND TRUE CACHE BOOL "Was Boost found?" FORCE)
@@ -42,5 +42,5 @@ ExternalProject_Get_Property( Boost source_dir )
 if(NOT Boost_INCLUDE_DIRS)
 	set( Boost_INCLUDE_DIRS ${source_dir} CACHE INTERNAL "Boost include directories")
 	# On Visual Studio Boost libs get automatically linked
-	message(STATUS "Downloading Boost automatically.")
+	message(STATUS "Downloading Boost ${OGS_BOOST_VERSION} automatically.")
 endif()

scripts/cmake/ThirdPartyLibVersions.cmake

-set(OGS_BOOST_URL "http://sourceforge.net/projects/boost/files/boost/1.58.0/boost_1_58_0.tar.bz2/download")
-set(OGS_BOOST_MD5 "b8839650e61e9c1c0a89f371dd475546")
+set(OGS_BOOST_VERSION 1.56.0)
+string(REPLACE "." "_" OGS_BOOST_VERSION_UNDERLINE ${OGS_BOOST_VERSION})
+set(OGS_BOOST_URL "http://sourceforge.net/projects/boost/files/boost/${OGS_BOOST_VERSION}/boost_${OGS_BOOST_VERSION_UNDERLINE}.tar.bz2/download")
+set(OGS_BOOST_MD5 "a744cf167b05d72335f27c88115f211d")
 
 set(OGS_EIGEN_URL "http://opengeosys.s3.amazonaws.com/ogs6-lib-sources/eigen-3.2.5.tar.gz")
 set(OGS_EIGEN_MD5 "8cc513ac6ec687117acadddfcacf551b")