Execute show repo command in repository directory

When cloning the repo for the first time, in "get" mode, the 
darcs_patchcount() function is executed in the darcs-src/ directory instead of
the darcs-src/$REPO directory. We should ensure the current directory is set
to the correct repository directory inside the function.

Signed-off-by: Vikraman Choudhury <vikraman@gentoo.org>