MIRA: Improve sorting of requirements
When an identifier of a requirement is a number it should be sorted accordingly (e.g. 1 should be sorted before 10). If numbers and strings are mixed, each numbers should be interpreted as a number and sorted before strings. The algorithm should work like the sorting of your file system.
e.g.:
2012_7_27_Fortiss
2012_12_07_AF3
1555630
20120726_Protokoll
A1
A10
(from redmine: issue id 1344, created on 2013-04-11, closed on 2013-06-25)