fix #2616: allow building of training data
fix #2616: allow building of training data

This fixes Issue #2616 by preventing an attempt to build the recognition engine when running tesstrain.sh.
amitdo/tesseract,UB-Mannheim/tesseract,tesseract-ocr/tesseract,tesseract-ocr/tesseract,stweil/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,tesseract-ocr/tesseract,stweil/tesseract,UB-Mannheim/tesseract,stweil/tesseract,UB-Mannheim/tesseract,UB-Mannheim/tesseract,stweil/tesseract,UB-Mannheim/tesseract,amitdo/tesseract,stweil/tesseract,amitdo/tesseract