svndump parses data that is in SVN dumpfile format produced by
`svnadmin dump` with the help of line_buffer and uses repo_tree and
fast_export to emit a git fast-import stream.

Based roughly on com.hydrografix.svndump 0.92 from the SvnToCCase
project at <http://svn2cc.sarovar.org/>, by Stefan Hegny and
others.

[rr: allow input from files other than stdin]
[jn: with test, more error reporting]
Signed-off-by: NDavid Barr <david.barr@cordelta.com>
Signed-off-by: NRamkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: NJonathan Nieder <jrnieder@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>