reflex (variant of flex fast lexical scanner)

This is Thomas E. Dickey's fork of flex, based on flex-2.5.4. It has
a few bugfixes and slightly different features from the flex included
in Slackware.

This build doesn't conflict with Slackware's flex. To build sources with
reflex, they'll have to be modified slightly:

- replace "flex" command with "reflex" in Makefiles or build scripts.
- replace any occurence of "-lfl" with "-lrefl".
- if the source includes <FlexLexer.h>, replace with <reFlexLexer.h>.