Rsync-bpc is a customized version of rsync that is used as part of
BackupPC, an open source backup system.

The main change to rsync is adding a shim layer (in the subdirectory
backuppc, and in bpc_sysCalls.c) that emulates the system calls for
accessing the file system so that rsync can directly read/write files
in BackupPC's format.

Rsync-bpc is fully line-compatible with vanilla rsync, so it can talk
to rsync servers and clients.

Rsync-bpc serves no purpose outside of BackupPC.