switch to rubygem() based buildrequires so we can easily switch the ruby version.

( pulled from https://build.suse.de/request/show/41434 )
fixed up an old changelog entry, added author
Merge branch 'darix'

Conflicts:
	package/yast2-devtools.changes
	package/yast2-devtools.spec

Resolved in favor of using
   rubygem(foo)
instead of
   rubygem(%{rb_default_ruby_abi}:foo)
version + changelog
Merge pull request #61 from yast/merge-ibs

Resolve IBS conflict.