Revision 1236284

AVRO-986. C/Java: Fixed relates to sync markers in file headers.

The C bindings no longer add an "avro.sync" entry to the header of an
Avro file.  (Previously, the Java bindings (at least) would barf if this
sync marker was present, since they'd treat that as the end of the file
header.)  The Java bindings now ignore the extra sync marker, if
present.

In addition, this patch adds a new "avromod" command-line utility to the
C bindings.  This utility can be used (among other things) to remove the
sync marker from the header of an existing file.  It works by copying
all of the records from a source file to a destination file.  You can
also override the block size and compression codec of the new
destination file.