Bump version to 2.9.1

The cycle will end on a 3.0 release instead of 2.2 as intended.
There are too many changes in the API to keep the same major number.

NEWS

@@ -1,7 +1,7 @@
-libmodbus 2.1.1 (2010-XX-XX)
+libmodbus 2.9.1 (2010-08-16)
 ============================
 
-- New API
+- Brand new API (see MIGRATION notes)!
 - Remove the internal function set_message_length_tcp
 - Restore slave ID (server ID) argument in functions
 - Error conventions of POSIX systems and error recover

configure.ac

@@ -12,7 +12,7 @@
 # http://www.gnu.org/software/libtool/manual/html_node/Libtool-versioning.html
 #
 m4_define([libmodbus_version_major], [2])
-m4_define([libmodbus_version_minor], [1])
+m4_define([libmodbus_version_minor], [9])
 m4_define([libmodbus_version_micro], [1])
 
 m4_define([libmodbus_release_status],