For an official release XCA_VERSION == PACKAGE_VERSION.
For any additional commit, XCA_VERSION's path-level is increased.
PACKAGE_VERSION cannot be modified after initially set.
Change any occurance of PACKAGE_VERSION by XCA_VERSION
The patchlevel will be increased by the iteration counter,
which is the number of commits since the most recent annotated tag.
Tagged version 1.2.3 in VERSION will be called "1.2.3"
3 commits later it will be 1.2.6
The plus sign was not compatible with the WIX toolset.
The 4th digist is the number of commits since the last release.
For a tagged release it is not 00, but empty.
