fix Issue 1223: TessPolyBlockType enum is outdated in C-API

git-svn-id: http://tesseract-ocr.googlecode.com/svn/trunk@1112 d0cd1f9f-072b-0410-8dd7-cf729c803f20
fix issue 1217: GetThresholdedImage accesses possibly NULL thresholder_

git-svn-id: http://tesseract-ocr.googlecode.com/svn/trunk@1113 d0cd1f9f-072b-0410-8dd7-cf729c803f20