add the "requires" option on Option object to create dependencies between options
according to Andrew Porokhin (@4ndrew) some refactoring
Since we already have @Option.required, I think it's better to name this bit differently to avoid confusion
made sure that aliases can be used
Merge branch 'pull-14'

Conflicts:
	args4j/src/org/kohsuke/args4j/Messages.java
	args4j/src/org/kohsuke/args4j/Messages.properties
	args4j/src/org/kohsuke/args4j/Option.java
TAB->WS