findHomagraphy can return empty Mat in master branch

Added erGrouping function: Find groups of Extremal Regions that are organized as text blocks. Updated sample/cpp to use the complete text detection pipeline

Streamlined mexext detection, with removal of trailing whitespace/newlines handled by execute_process

first parameter of createERFilterNM1/createERFilterNM2 is now mandatory. changed the sample program to use the new prototypes

renamed getDefaultClassifierNM{1,2}() to loadClassifierNM{1,2}() and added "const std::string& filename" parameter (mandatory).

functions getDefaultClassifierNM1() and getDefaultClassifierNM2() allow to implicitly load the default classifiers when creating a ERFilter object

fix thin-prism coefficients at 0's in the stereo calibration function unless the flag CALIB_THIN_PRISM_MODEL is explicitly set

I didn't make the status part of the version variables here, because
letters don't play too well with version comparison algorithms
(especially with CMake's, which only supports numbers).