Allow for compilation of ruleflow files with *.rf extension.

The Drools-Ant taks currently compiles *.rfm ruleflow files. Please compile also *.rf files.
http://fisheye.jboss.com/browse/JBossRules/trunk/drools-ant/src/main/java/org/drools/contrib/DroolsCompilerAntTask.java?r=21644#l54

I believe .rfm was the old format that is no longer used in Drools 5.

Workaround is to change the extension to .rfm however, the eclipse ruleflow plugin doesn't recognize this file type.

Thank you.