Fix generation of LibeventConfig.cmake for the installation tree

'LIBEVENT_INCLUDE_DIRS' is properly initialized in 'LibeventConfig.cmake' as
'LibeventConfig.cmake.in' contains usage of 'LIBEVENT_CMAKE_DIR' and
'EVENT_INSTALL_INCLUDE_DIR' variables but not 'EVENT_CMAKE_DIR' and
'EVENT__INCLUDE_DIRS'.
Related typos are fixed.

CMakeLists.txt

@@ -1324,11 +1324,11 @@ file(RELATIVE_PATH
      "${EVENT_INSTALL_CMAKE_DIR}"
      "${CMAKE_INSTALL_PREFIX}/include")
 
-# Note the EVENT_CMAKE_DIR is defined in LibeventConfig.cmake.in,
+# Note the LIBEVENT_CMAKE_DIR is defined in LibeventConfig.cmake.in,
 # we escape it here so it's evaluated when it is included instead
-# so that the include dirs are givenrelative to where the
+# so that the include dirs are given relative to where the
 # config file is located.
-set(EVENT__INCLUDE_DIRS "\${EVENT_CMAKE_DIR}/${REL_INCLUDE_DIR}")
+set(EVENT_INSTALL_INCLUDE_DIR "\${LIBEVENT_CMAKE_DIR}/${REL_INCLUDE_DIR}")
 
 configure_file(${PROJECT_SOURCE_DIR}/cmake/LibeventConfig.cmake.in
                ${PROJECT_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/LibeventConfig.cmake