Fixed several issues with empty arrays etc. and with inconsistent behaviour of some modules.
Added possibility to crop frames detected too close the image border.

This feature has been added because of synthetic dataset where
the transformed image data do not fill the whole image plane.
Therefore a lot of border effects are present and this removes
features which may be influenced by them.
Updated default VLFeat version.
Fixed unpack for .tar archives.
Added possibility to generate general anisotropy and a temporary workaround to keep order of transformations.
Added helper function for to linearise homography in a point.

Author of the code: Kristian Mikolajczyk.
Merge branch 'unstable' of github.com:vlfeat/vlbenchmarks into unstable