replace relative csync buildir detection magic

If you do not want to run make install for lib(o)csync,
pass -DCSYNC_LIBRARY_PATH=$your_csync_builddir
and  -DCSYNC_INCLUDE_PATH=$your_csync_srcdir/src
to cmake when building mirall.

cmake/modules/FindCsync.cmake

@@ -4,11 +4,11 @@ ELSE()
   FIND_PATH(CSYNC_INCLUDE_PATH NAMES csync.h HINTS $ENV{CSYNC_DIR} )
 ENDIF()
 
-IF(EXISTS "${CMAKE_SOURCE_DIR}/../buildcsync/src/")
+IF( DEFINED CSYNC_LIBRARY_PATH AND DEFINED CSYNC_INCLUDE_PATH )
   IF( WIN32 )
-     SET(CSYNC_LIBRARY ${CMAKE_SOURCE_DIR}/../win/buildcsync/src/libocsync.dll)
+    SET(CSYNC_LIBRARY ${CMAKE_SOURCE_DIR}/src/libocsync.dll)
   ELSE( WIN32 )
-     SET(CSYNC_LIBRARY ${CMAKE_SOURCE_DIR}/../buildcsync/src/libocsync.so)
+    SET(CSYNC_LIBRARY ${CSYNC_LIBRARY}/src/libocsync.so)
   ENDIF( WIN32 )
 ELSE()
   FIND_LIBRARY(CSYNC_LIBRARY NAMES ocsync HINTS $ENV{CSYNC_DIR})