Add Debian sid build pass (#4707)

* Add Debian sid build pass

* Update file locations and copyright

* Use ccache

* Redirect within sudo

* Work around a pbuilder bug which breaks ccache

* Debian: enable parallel builds

* Travis: Debian: fix caching

* Fix shellcheck warnings

cmake/modules/BashCompletion.cmake

@@ -73,9 +73,10 @@ ELSE()
 		FILE(WRITE ${BASHCOMP_SCRIPT} "\
 #!${BASH}\n\
 set -e\n\
-BASHCOMP_PKG_PATH=\"${BASHCOMP_USER_PATH}\"\n\
 if [ -w \"${BASHCOMP_PKG_PATH}\" ]; then\n\
   BASHCOMP_PKG_PATH=\"${BASHCOMP_PKG_PATH}\"\n\
+else \n\
+  BASHCOMP_PKG_PATH=\"\$DESTDIR${BASHCOMP_USER_PATH}\"\n\
 fi\n\
 echo -e \"\\nInstalling bash completion...\\n\"\n\
 mkdir -p \"\$BASHCOMP_PKG_PATH\"\n\