build.bat: Call update_version.bat when using /GetVersion switch to make
sure that we get current data.

Additionally change the way how data is extracted from files. This
resolves build.bat fail when we are in detached git mode and branch is
reported as ("no branch").
build.bat: cosmetics
Merge pull request #55 from kasper93/batch

build.bat improvements
Mpeg2DecFilter.cpp: fix a useless dereference
Initialize variables in the constructor.
Cppcheck fixes:

* reduce variable scope
* remove unneeded variable assignments
update contrib/icl13.diff