CMake finds correct Eigen config in Ubuntu 14.04.

The installation tutorial instructs to install Eigen3.  A standard
Ubuntu installation has no FindEigen.cmake, but only FindEigen3.cmake.
Therefore, I instructed CMake to require Eigen3 instead of Eigen.
Compatibility update for ROS Indigo.

CvBridge does not have the imgmsg_to_cv function anymore, but it is
renamed to imgmsg_to_cv2.
kalibr_bagcreater can now handle short filenames.

Previously, filenames had to be at least 10 character, without filetype
extension.  When a filename was shorter, an empty string would be passed
to int(), which results in a ValueError.  With this version, when an
empty string is encountered, secs is set to 0.
Merge branches 'indigo-compatibility' and 'eigen-ubuntu' of github.com:pkok/kalibr
Grayscale images sometimes problem in calibration.

When the sensor_msgs/Image is converted to its numpy `ndarray`
representation, it sometimes has the shape `(n, m, 1)`.  This gives an
error even though it is a `sensor_msgs::image_encodings::MONO8`.

The underlying algorithm only supports 2D arrays, and the images were
stored as 3D objects.  Error:

```
TypeError: Conversion is only valid for arrays with 1 or 2
dimensions. Argument has 3 dimensions
```

Transforming the image with a reshape if and only if it has a dimension
of lenght 1 solves this problem.
Merge branch 'kalibr_target_extractor'
Merge remote-tracking branch 'remotes/pkok/master'