configure.ac: fix the flex error message

Per Paul Hargrove's email
(http://www.open-mpi.org/community/lists/devel/2015/04/17310.php),
there were a few typos in the message displayed when flex is not
found.  Additionally, somehow it didn't show the list of *.l files on
his system.  This is not a super-important message -- so just take
that "find" out (and force developers to install flex).

configure.ac

@@ -994,29 +994,21 @@ AC_PROG_EGREP
 AM_PROG_AS
 AM_PROG_LEX
 
-# If we don't have GNU Flex and we don't have a generated .c file
-# (distribution tarballs will have the .c file included, but SVN
-# checkouts will not), then error.  Must have GNU Flex -- other
-# versions of Lex are not workable (all things being equal, since this
-# is *only* required for developers, we decided that it really was not
-# worth it to be portable between different versions of lex ;-).
+# If we don't have Flex and we don't have a generated .c file
+# (distribution tarballs will have the .c file included, but git
+# clones will not), then error.  Must have Flex -- other versions of
+# Lex are not workable (all things being equal, since this is *only*
+# required for developers, we decided that it really was not worth it
+# to be portable between different versions of lex ;-).
 
 if test -z "$LEX" || \
    test -n "`echo $LEX | $GREP missing`" || \
    test "`basename $LEX`" != "flex"; then
     if test ! -f "$srcdir/opal/util/show_help_lex.c"; then
-        AC_MSG_WARN([*** Could not find GNU Flex on your system.])
-        AC_MSG_WARN([*** GNU Flex required for developer builds of Open MPI.])
+        AC_MSG_WARN([*** Could not find Flex on your system.])
+        AC_MSG_WARN([*** Flex is required for developer builds of Open MPI.])
         AC_MSG_WARN([*** Other versions of Lex are not supported.])
-        AC_MSG_WARN([*** YOU DO NOT NEED FLEX FOR DISTRIBUTION TARBALLS!])
-        AC_MSG_WARN([*** If you absolutely cannot install GNU Flex on this system])
-        AC_MSG_WARN([*** consider using a distribution tarball, or generate the])
-        AC_MSG_WARN([*** following files on another system (using Flex) and])
-        AC_MSG_WARN([*** copy them here:])
-        for lfile in `find . -name \*.l -print`; do
-            cfile="`echo $lfile | cut -d. -f-2`"
-            AC_MSG_WARN([***     $cfile.c])
-        done
+        AC_MSG_WARN([*** YOU DO NOT NEED FLEX WHEN BUILDING DISTRIBUTION TARBALLS!])
         AC_MSG_ERROR([Cannot continue])
     fi
 fi