Revert "remove lib/versionstring.h on distclean"
Revert "remove lib/versionstring.h on distclean"

This reverts commit c8e5d1c767cd3f08adacdc84e204ed116e02d2ca.

Releases contain lib/versionstring.h and this file is just once auto
generated before releases. So removing it in distclean will require to
unpack the tarball again -> not a good idea.

shogun-toolbox/shogun,lambday/shogun,shogun-toolbox/shogun,sorig/shogun,Saurabh7/shogun,Saurabh7/shogun,lambday/shogun,karlnapf/shogun,geektoni/shogun,lisitsyn/shogun,lisitsyn/shogun,sorig/shogun,karlnapf/shogun,Saurabh7/shogun,shogun-toolbox/shogun,sorig/shogun,lisitsyn/shogun,geektoni/shogun,lisitsyn/shogun,lisitsyn/shogun,sorig/shogun,lisitsyn/shogun,sorig/shogun,geektoni/shogun,Saurabh7/shogun,geektoni/shogun,karlnapf/shogun,besser82/shogun,besser82/shogun,Saurabh7/shogun,Saurabh7/shogun,Saurabh7/shogun,sorig/shogun,besser82/shogun,Saurabh7/shogun,geektoni/shogun,karlnapf/shogun,shogun-toolbox/shogun,Saurabh7/shogun,lambday/shogun,besser82/shogun,geektoni/shogun,karlnapf/shogun,karlnapf/shogun,besser82/shogun,lambday/shogun,lambday/shogun,shogun-toolbox/shogun,lambday/shogun,besser82/shogun,shogun-toolbox/shogun