Use _split_longopt in _dpkg.

CHANGES

@@ -38,7 +38,7 @@ bash-completion (1.x)
   * Add _split_longopt() helper for improved handling of long options that
     take arguments in both "--foo bar" and "--foo=bar" formats.
   * Use _split_longopt to improve and clean up aspell, chgrp, chown, chkconfig,
-    cpio, iptables, make, mc, mii-diag, mii-tool, mkinitrd, postgresql,
+    cpio, dpkg, iptables, make, mc, mii-diag, mii-tool, mkinitrd, postgresql,
     quota, samba, smartctl, and generic long option completion
     (Alioth: #311398).
   * Add chown --from and --reference value completions.

bash_completion

@@ -2932,6 +2932,8 @@ _dpkg()
 
 	_expand || return 0
 
+	_split_longopt
+
 	# find the last option flag
 	if [[ $cur != -* ]]; then
 		while [[ $prev != -* && $i != 1 ]]; do
@@ -2981,13 +2983,13 @@ _dpkg()
 			--force-confmiss --force-conflicts --force-architecture\
 			--force-overwrite-dir --force-remove-reinstreq \
 			--force-remove-essential -Dh \
-			--debug=help --licence --admindir= --root= --instdir= \
+			--debug=help --licence --admindir --root --instdir \
 			-O --selected-only -E --skip-same-version \
 			-G --refuse-downgrade -B --auto-deconfigure \
-			--no-debsig --no-act -D --debug= --status-fd \
+			--no-debsig --no-act -D --debug --status-fd \
 			-b --build -I --info -f --field -c --contents \
 			-x --extract -X --vextract --fsys-tarfile -e --control \
-			--ignore-depends= --abort-after' -- $cur ) )
+			--ignore-depends --abort-after' -- $cur ) )
 		;;
 	esac