since at least 5c2ba4aa flex 2.5.35 or
newer is required, but linux baseline (CentOS 5.9) shippes with older
one. Fail in configure/autogen instead of during make
Signed-off-by: Stephan Bergmann <sbergman@redhat.com>
...and gracefully cope with Mac OS X flex --version returning "flex 2.5.35
Apple(flex-31)", so just look for the first run of d.d.d when determining the
version number

Change-Id: Ia5a324474aaa1a45910f50b4a78ab6ce6279575e