Update largefile.test for optional more repeatable testing.
Update largefile.test for optional more repeatable testing.

Allow "blocks" to be specified in $2 for different sized files and
also to enable more persistent test data to make testing more
repeatable.

yrgoldteeth/librsync,yrgoldteeth/librsync,yrgoldteeth/librsync,librsync/librsync,dbaarda/librsync,sourcefrog/librsync,sourcefrog/librsync,dbaarda/librsync,sourcefrog/librsync,yrgoldteeth/librsync,librsync/librsync,librsync/librsync,librsync/librsync,dbaarda/librsync,dbaarda/librsync,sourcefrog/librsync