Bugfix 3306

More info: http://code.opencv.org/issues/3306
Applied fixes for the interface of image sequence reading.
It is available in openCV 2.4.7 source code but not documented.

Basically the line is scanned in opposite direction now, in order not to cope with specific formatting in the rest of the string.

Have supplied a pull request to master in the past, but master also contains errors.
Will provide fix in seperate pull request. (https://github.com/Itseez/opencv/pull/1846)