[PATCH] svnrdump "help" displays subcommand-specific documentation

Hi,

This patch makes the "svnrdump's" help to display the
subcommand-specific documentation.
( similar to "svn", "svnlook", "svnadmin" ...)

 Previously, "svnrdump dump --help" does *not* display the
help-documentation corresponding to "dump", but "svnrdump help dump" did
as expected.

Meanwhile, few other observations in the *current* behaviour are :

1. The "svnrdump" does *not* display the generic documentation as
follows...

" Type 'svn --version' to see the program version and RA modules "

eventhough it supports "svnrdump --version".

2. "svnrdump --version --junk" also displays the version documentation,
which it should *not*.

I am working on these observations to make them behave uniformly and
will come up in further patches.

I have attached the patch and the log file with this mail.

Thanks and regards
Prabhu