* fixed Github Issue #36 (reported by opax)
* bugfix for FileSubmissionHandler, writing to stream depended on logging (thx opax for finding the bug in first place)
More robust error logging in ErrorServlet

There were several cases where internal processing in the ErrorServlet would throw an exception, resulting in the overly broad (and often wrong) message „XFormsException: Prefix xf has not been declared“ in the log.

This patch logs whatever information has been collected up to the point of the exception, resulting in much more helpful messages. It also uses LOGGER to output the error document instead of dumping it to System.out .
Merge pull request #37 from opax/error-logging

More robust error logging in ErrorServlet
removed non-ascii chars in source files
removed possible NPEs
more consistent logging

- avoid System.out
- more robust error logging in ErrorServlet
unified logging, helper functions to log DOMs
update maven pom to use the same java language level as ant
removed possible NPEs
fixed NPEs