handle Attic-only RCS files over CVS pserver

CVS repositories may contain RCS history in file,v as well as
a corresponding Attic/file,v where each file contains separate
events that occurred in history. The Attic version of the file
results from file deletion events.

The rsync access method already uses history found in the Attic.
However, a CVS server will only return RCS files from the Attic
if we request them explicitly. If we do not request them then our
converted history may end up missing deletion events for some files.
Unfortunately, we cannot tell which RCS files have a corresponding
file in the Attic, so we need to search all Attic directories by
running the equivalent of 'cvs rlog' in each directory. This slows
down pserver access considerably (and it was already quite slow
compared to rsync). But we need to pay this price in order to
obtain a valid conversion result.

This patch contains related fixes to cvsroot path handling, which
was broken for the pserver case. Without these fixes we cannot
create the correct paths for Attic directories to search.

Problem found while comparing conversion results of rsync and
pserver access methods for the GNU dino CVS repository at
cvs.savannah.gnu.org/sources/dino
Add two new test cases based on RCS files from this repository.

Without this fix in place history would diverge at this commit:

8891a63 | larsl | Removed the MIDIEvent class | 04 May 2006, 01:11 UTC

Because the files midievent.cpp and midievent.hpp would not get deleted
when converting this commit via the pserver protocol.