cb-plugin: remove `public' specifier from most classes.

package: check for filename length.
Merge RegionBreak and RegionMerge to RegionFile.
lz4: decompressor security fix.
correct specification file.
lz4-java: change constructor visibility to private.
Merge branch 'master' of s1.linnaea.name:MCBackup
cb-plugin: keep delta backup when rebasing.

build: specify versions for dependencies to speed up build.
nitpick: remove extra newline in BackupTree.Root.toString()
cb-plugin: handle backups with same timestamps properly in GC
remove BiasedSeekableInputStream
fix GC when there's no duplicate backup
upstream(lz4/xxhash): strict prototype definition
build: impose 180 sec timeout when downloading latest bukkit jar.
[defconf] freq.backup: 7200 --> 28800