Generator : unable to distinguish real errors

The bin/nutch generate command is returning the same error code (-1) if there is an error or no new segment to process, so there is no way to tell if the error is real or not from a shell script. This problem is related to NUTCH-1828.

The problem can be fixed by modifying the following Java source file:
http://svn.apache.org/viewvc/nutch/trunk/src/java/org/apache/nutch/crawl/Generator.java?revision=1619934&view=markup

At line 711, if there are no new segment, the generator returns -1, which is the same return code returned at line 714 if there was an error.