Use relative paths in cscope.files

This is to avoid duplicates with auto-includes of header files from
cscope
Free marker when unused
Try reuse existing window to display result

When displaying result in "other window", result buffer needs to be quit
first because it has been displayed itself in an other window
Fix default-directory
Fix relative paths with tramp

Signed-off-by: Sylvain Chouleur <sylvain.chouleur@gmail.com>
Merge remote-tracking branch 'remotes/origin/free_marker' into merging
Merge remote-tracking branch 'remotes/origin/reuse_window' into merging