Take git info out of BUILD_INFO, prepare for tarball export
Added source-dist make target

source-dist is a make target for creating a standalone tarball that can
be compilled on a system with the requisit external dependencies without
internet access to download the internal dependencies.
Changed BUILD_INFO to GIT_VERSION_INFO in methodsshow
Checked inn readline patches, instad of downloading them

I can not see why we download the readline patches, and it requires
somewhat  ugly code in the make rule for the source-dist target.
Merge pull request #5528 from ivarne/distributing

make source-dist + git version info separation