FS backends comparison

[Daniel Shahaf]

http://svnbook.red-bean.com/en/1.7/svn.reposadmin.planning.html#svn.reposadmin.basics.backends.tbl-1

Three comments:

1. FSFS "Number of revision trees" - doesn't account for the sharding
feature

2. In the 1.8 book, the table should mention that BDB is deprecated

3. A user on #svn reports:
<rudrab> as in redbook, it is said that the default fsfs is not as reliable
which goes to the "Data integrity" item.

Perhaps we can change that item to talk about the current/future
versions rather than about past versions?  e.g., "FSFS[Data Integrity]:
in-house database format, so higher likelihood of inability to
deserialize after svn_fs_commit_txn() returns" (okay, but with less
technical terms :-))

Daniel