USE GNUInstallDirs to fix man page and multilib install

See also: http://dev.exiv2.org/issues/1125
Patch based on: http://pkgs.fedoraproject.org/cgit/exiv2.git/tree/exiv2-0.25-cmake_LIB_SUFFIX.patch

--- b/config/CMakeChecks.txt	2015-07-19 14:23:11.606686135 +0200
+++ b/config/CMakeChecks.txt	2015-06-22 08:41:22.913094633 -0500
@@ -37,6 +37,8 @@
 INCLUDE( CheckCSourceCompiles )
 INCLUDE( CheckCXXSourceCompiles )
 
+INCLUDE( GNUInstallDirs )
+
 INCLUDE( FindIconv )
 
 SET( STDC_HEADERS ON )
@@ -289,9 +291,9 @@
 
 IF( NOT MSVC )
     CONFIGURE_FILE( config/exiv2.pc.cmake ${CMAKE_CURRENT_BINARY_DIR}/exiv2.pc @ONLY )
-    INSTALL( FILES ${CMAKE_CURRENT_BINARY_DIR}/exiv2.pc DESTINATION lib/pkgconfig )
+    INSTALL( FILES ${CMAKE_CURRENT_BINARY_DIR}/exiv2.pc DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig )
     CONFIGURE_FILE( config/exiv2.lsm.cmake ${CMAKE_CURRENT_BINARY_DIR}/exiv2.lsm)
-    INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/exiv2.lsm DESTINATION lib/pkgconfig )
+    INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/exiv2.lsm DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig )
 ENDIF( NOT MSVC )
 
 # ******************************************************************************
--- a/src/CMakeLists.txt	2015-07-19 14:06:54.104906589 +0200
+++ b/src/CMakeLists.txt	2015-07-19 14:12:37.982607526 +0200
@@ -321,7 +321,7 @@
 
 # ******************************************************************************
 # Man page
-INSTALL( FILES exiv2.1 DESTINATION man/man1 )
+INSTALL( FILES exiv2.1 DESTINATION ${CMAKE_INSTALL_MANDIR}/man1 )
 
 # That's all Folks!
 ##
--- a/CMakeLists.txt	2015-06-15 10:32:21.000000000 -0500
+++ b/CMakeLists.txt	2015-06-22 08:48:19.486245765 -0500
@@ -25,7 +25,7 @@ if( POLICY CMP0042 )
 else()
     SET(CMAKE_MACOSX_RPATH 1)
 endif()
-SET(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")
+#SET(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}")
 
 
 SET( PACKAGE_COPYRIGHT      "Andreas Huggel" )
@@ -156,10 +156,10 @@ INCLUDE( config/CMakeChecks.txt )
 
 SET( INSTALL_TARGET_STANDARD_ARGS
      RUNTIME DESTINATION bin
-     LIBRARY DESTINATION lib
-     ARCHIVE DESTINATION lib
+     LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+     ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
 )
-SET(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")
+#SET(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}")
 
 ##
 # add sources from XMPSDK directory