Read matlab mat files using matio library

[TimSC]

I don't have access to the MatlabIO library, so I have attempted to read mat files using the open source matio library. This addresses issue #14. This is almost working but there are problems in FileStorageModel.cpp:

./ModelTransfer test7.mat ../../matlab/Demo_model.xml
-------------------------------
        Model Transfer         
-------------------------------

deserializing Matlab (.mat) model...
converting...
serializing to OpenCV (.xml) model...
OpenCV Error: Bad argument (An attempt to add element without a key to a map, or add element with key to sequence) in icvXMLWriteTag, file /build/buildd/opencv-2.3.1/modules/core/src/persistence.cpp, line 2229
terminate called after throwing an instance of 'cv::Exception'
  what():  /build/buildd/opencv-2.3.1/modules/core/src/persistence.cpp:2229: error: (-5) An attempt to add element without a key to a map, or add element with key to sequence in function icvXMLWriteTag

Aborted

This might be caused by my old version of OpenCV or a bug someone else. As far as I can tell, the mat file is correctly read into memory but I could really do with a known "good" mat file the correctly converts in ModelTransfer with MatlabIO enabled. Anyone?

Also, some additional work is needed in the CMake files in cases where matio is not installed. I am not sure how to do that.

Note that matio only reads matlab files and does not read Octave mat files in the default mode (however Octave can save in a matlab format)