Fix MODELLO-284 and MODELLO-285

Fix two bugs:
* MODELLO-284: Generated StAX reader fails to compile if model has any Boolean fields.
* MODELLO-285: Generated StAX reader fails to compile if adders are explicitly disabled.

http://jira.codehaus.org/browse/MODELLO-284
http://jira.codehaus.org/browse/MODELLO-285