Update pgindent instructions to avoid changes to flex output files.

src/tools/pgindent/README

-$PostgreSQL: pgsql/src/tools/pgindent/README,v 1.31 2009/06/10 01:51:44 momjian Exp $
+$PostgreSQL: pgsql/src/tools/pgindent/README,v 1.32 2010/02/26 01:40:15 momjian Exp $
 
 pgindent
 ========
@@ -17,6 +17,11 @@ This can format all PostgreSQL *.c and *.h files, but excludes *.y, and
 	egrep -v '/s_lock.h|/ecpg/test/expected/|/snowball/libstemmer/' |
 	xargs -n100 pgindent /tmp/typedefs.pl
 
+3) pgindent cannot process the YY_INPUT macro generated by flex, so remove
+   the generate C files so they are rebuilt:
+
+	rm -f $(find . -type f -name '*.l' -print | sed 's/l$/c/')
+
 
 ---------------------------------------------------------------------------
 
@@ -42,6 +47,8 @@ src/include/snowball/libstemmer/ and src/backend/snowball/libstemmer/
 are excluded because those files are imported from an external project,
 not maintained locally, and are machine-generated anyway.
 
+YY_INPUT
+
 ---------------------------------------------------------------------------
 
 Obsolete typedef list creation instructions: