fix installation of main module headers

see: http://code.opencv.org/issues/2897

The order of the 2 conditions is really important, as every MATCHES
operator sets ${CMAKE_MATCH_1}, which is needed inside the condition
block. Ideally, this should be done using a single regex with a
negative forward lookahead, but CMake doesn't seem to support this

cmake/OpenCVModule.cmake

@@ -535,7 +535,7 @@ macro(ocv_create_module)
   if(OPENCV_MODULE_${the_module}_HEADERS AND ";${OPENCV_MODULES_PUBLIC};" MATCHES ";${the_module};")
     foreach(hdr ${OPENCV_MODULE_${the_module}_HEADERS})
       string(REGEX REPLACE "^.*opencv2/" "opencv2/" hdr2 "${hdr}")
-      if(hdr2 MATCHES "^(opencv2/.*)[^/]+.h(..)?$" AND NOT hdr2 MATCHES "opencv2/${the_module}/private.*")
+      if(NOT hdr2 MATCHES "opencv2/${the_module}/private.*" AND hdr2 MATCHES "^(opencv2/?.*)/[^/]+.h(..)?$" )
         install(FILES ${hdr} DESTINATION "${OPENCV_INCLUDE_INSTALL_PATH}/${CMAKE_MATCH_1}" COMPONENT main)
       endif()
     endforeach()