minor bug with latest flex

Running ./configure with CVS HEAD on my machine yields:

checking for gawk... no
checking for mawk... mawk
checking for flex... no
configure: WARNING:
*** The Flex version 2.5.3 you have at /usr/bin/lex contains a bug. You
*** should get version 2.5.4 or later.
configure: WARNING:
*** Without Flex you will not be able to build PostgreSQL from CVS or
*** change any of the scanner definition files. You can obtain Flex
from
*** a GNU mirror site. (If you are using the official distribution of
*** PostgreSQL then you do not need to worry about this because the Flex
*** output is pre-generated.)

But the flex version check seems a little inaccurate:

$ flex --version
flex 2.5.31

Cheers,

Neil