ACCUMULO-1814 Fixes WALog reading issue from 1.5

WALogs from 1.5.0 use a slightly different format than WALogs
from 1.6.0.  Consequently, the code to read WALogs from 1.6.0
doesn't work on files from 1.5.0.  I made changes to
DFSLogger to correctly interpret 1.5.0 based log files,
and increments the log version number to 3, so that
the WALog reading code can correctly identify what type of
file we're dealing with.

This may still require more testing especially with encryption
turned on but for now this will do.

Signed-off-by: Eric Newton <eric.newton@gmail.com>
ACCUMULO-1587 add 'print to file' for grep
Merge branch '1.5.1-SNAPSHOT'

Conflicts:
	core/src/main/java/org/apache/accumulo/core/util/shell/commands/ScanCommand.java