git-svn: fix SVN 1.1.x compatibility

git-svn: fix SVN 1.1.x compatibility

The get_log() function in the Perl SVN API introduced the limit
parameter in 1.2.0.  However, this got discarded in our SVN::Ra
compatibility layer when used with SVN 1.1.x.  We now emulate
the limit functionality in older SVN versions by preventing the
original callback from being called if the given limit has been
reached.  This emulation is less bandwidth efficient, but SVN
1.1.x is becoming rarer now.

Additionally, the --limit parameter in svn(1) uses the
aforementioned get_log() functionality change in SVN 1.2.x.
t9129 no longer depends on --limit to work and instead uses
Perl to parse out the commit message.

Thanks to Tom G. Christensen for the bug report.

Signed-off-by: Eric Wong <normalperson@yhbt.net>