debian/rules: Some extra quotes. Reduce delta between upstream DEB packaging and official Debian package.

 0001_nxagent-Determine-nxagentProgName-only-once.patch
 0002_nxdialog-bin-nxdialog-Fix-error-dialog-type-not-supp.patch
 0003_xkbUtils.c-Catch-division-by-zero.patch
 0004_libNX_X11-add-additional-checks-for-dpy-and-xkb.patch
 2004_enforce-lpthread.patch

debian/patches: Add 0003_xkbUtils.c-Catch-division-by-zero.patch. Catch occasional division-by-zero error. (Closes: #929498). Add 0004_libNX_X11-add-additional-checks-for-dpy-and-xkb.patch. Don't reference dpy nor xkb if undefined. (Closes: #929499).

debian/patches: Add 0001_nxagent-Determine-nxagentProgName-only-once.patch. Keep branding flavour (i.e., running as nxagent or x2goagent) after session resumptions. (Closes: #928760). Add 0002_nxdialog-bin-nxdialog-Fix-error-dialog-type-not-supp.patch. Cosmetic fix in nxdialog's error output.

debian/patches: Add 2004_enforce-lpthread.patch. On Debian, enforce -lpthread when building nxcomp. This is a nasty work around for a missing symbols issue that needs to get addressed otherwise in a later upstream release. (Closes: #922293).

debian/{control,compat}: Drop compat file. Switch over to debhelper-compat notation in control file. Bump DH compat level to version 12.