CMake subproject support, part 1: use project-relative paths.

Otherwise it would reference directory relative to source root and not
project root, which is not always the same.

CMakeLists.txt

@@ -27,7 +27,7 @@ cmake_minimum_required(VERSION 2.8.9)
 project(Magnum)
 
 # Find Corrade first so we can check on the target
-set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/modules/")
+set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${PROJECT_SOURCE_DIR}/modules/")
 find_package(Corrade REQUIRED)
 
 include(CMakeDependentOption)

doc/generated/CMakeLists.txt

@@ -26,7 +26,7 @@
 cmake_minimum_required(VERSION 2.8.9)
 project(MyApplication)
 
-set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/../../modules/")
+set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${PROJECT_SOURCE_DIR}/../../modules/")
 
 find_package(Magnum REQUIRED
     MeshTools

doc/getting-started.dox

@@ -86,7 +86,7 @@ subdirectory.
 cmake_minimum_required(VERSION 2.8.9)
 project(MyApplication)
 
-set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/modules/")
+set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${PROJECT_SOURCE_DIR}/modules/")
 
 add_subdirectory(src)
 @endcode

src/CMakeLists.txt

@@ -47,7 +47,7 @@ include_directories(${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_BINARY_DIR} ${CO
 # We can use both implicit include path (GLES2/gl2.h) where our headers can
 # be overriden with system ones or explicit (MagnumExternal/OpenGL/GLES2/gl2ext.h)
 # where only our headers will be used
-include_directories(${CMAKE_SOURCE_DIR}/src/MagnumExternal/OpenGL)
+include_directories(${PROJECT_SOURCE_DIR}/src/MagnumExternal/OpenGL)
 
 add_subdirectory(MagnumExternal)
 add_subdirectory(Magnum)