Add check for dimension of a merged file

[HealthyPear]

could be as simple checking that it is greater than the last single file or the more precise check its equal to the sum of the single files of the bunch

NOTE there could be a problem if one or more of the files in the bunch is not processed at the next level (e.g. the simtel file is corrupt)

[HealthyPear]

This has been solved by #51 and #50. Closing.