flex: Add local modifications and DragonFly READMEs

flex: Add local modifications and DragonFly READMEs

The quality of the latest flex 2.5.37 release is pretty poor.  The
man page displayed the wrong version, the code doesn't compile with
GCC 4.7, the new lerrs_fatal function missing a protocol and then
given the wrong type once when it was called.  Some of the errors
could have been fixed with higher WARNS settings but these patches
applied over the flex vendor branch should fix the bugs.

The standard DragonFly README files are added at the same time.