Add largefile.test for testing with large files.
Add largefile.test for testing with large files.

Note this test is not included in "make check" because it creates very
large data files and takes a long time.

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