rscope: fix relative paths with tramp

Fix relative cscope files in the tramp usecase.

Signed-off-by: Sylvain Chouleur <sylvain.chouleur@gmail.com>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
rscope: raise an error on cscope database generation failure

Instead of letting an unnoticed error pass by and report a "cannot init
database", report the error returned by the cscope process.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>