Allow consumers to enforce using namespaced includes

Setting QUOTIENT_FORCE_NAMESPACED_INCLUDES before the find_package
call will not add the namespace include dir to the search path.

This isn't really elegant, but allows both retaining full source
compatibility and helps consumers that have clashing include file
names.

CMakeLists.txt

@@ -316,7 +316,6 @@ target_include_directories(${PROJECT_NAME} PUBLIC
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/Quotient>
     $<INSTALL_INTERFACE:${${PROJECT_NAME}_INSTALL_INCLUDEDIR}>
-    $<INSTALL_INTERFACE:${${PROJECT_NAME}_INSTALL_INCLUDEDIR}/Quotient>
 )
 
 target_link_libraries(${PROJECT_NAME} PUBLIC ${Qt}::Core ${Qt}::Network ${Qt}::Gui qt${${Qt}Core_VERSION_MAJOR}keychain)

cmake/QuotientConfig.cmake.in

@@ -3,3 +3,9 @@ include(CMakeFindDependencyMacro)
 @FIND_DEPS@
 
 include("${CMAKE_CURRENT_LIST_DIR}/QuotientTargets.cmake")
+
+if (NOT QUOTIENT_FORCE_NAMESPACED_INCLUDES)
+    get_target_property(_include_dir @PROJECT_NAME@ INTERFACE_INCLUDE_DIRECTORIES)
+    list(APPEND _include_dir "${_include_dir}/Quotient")
+    set_target_properties(@PROJECT_NAME@ PROPERTIES INTERFACE_INCLUDE_DIRECTORIES "${_include_dir}")
+endif()