Issue #2231: Attempt to fix segfault, when copying labels. LDA needed to be updated to generate the Wrapper correctly.

Exceptions now go into CV_Error. Added thresholding to the FaceRecognizer and updated the demo accordingly.

Several exceptions added to the available FaceRecognizer classes and helper methods, so wrong input data is reported to the user. facerec_demo.cpp updated to latest cv::Algorithm changes and commented.

Merged lda fix from 2.4 branch (Fixed reconstruction, so that the mean is correctly added to the reconstructed image.)