Do parallel builds for Ubuntu packages

Make the builds faster as we now run them often via Travis.

contrib/packages/deb/ubuntu-trusty/debian/rules

 
 export CFLAGS CPPFLAGS CXXFLAGS LDFLAGS
 
+NUMJOBS := -j$(shell nproc)
+
 # Uncomment this to turn on verbose mode. 
 #export DH_VERBOSE=1
 
 	(cd fltk-*;DSOFLAGS="$(filter-out -fPIE -pie,$(LDFLAGS))" \
     ./configure --enable-shared=no --enable-cairo --enable-cp936 \
     --with-optim="$(CFLAGS) $(XCFLAGS)" --libdir=$(libdir))
-	make -C fltk-*
+	make $(NUMJOBS) -C fltk-*
 	touch fltk-stamp
 
 configure: config-stamp
 	# Add here command to compile/build the package.
 	# Build first things.
 	# Build Xvnc
-	make LDFLAGS="-lpng" 
-	(cd unix/xserver;make)
+	make $(NUMJOBS) LDFLAGS="-lpng"
+	make $(NUMJOBS) -C unix/xserver
 
 	touch build-arch-stamp
 

contrib/packages/deb/ubuntu-xenial/debian/rules

 
 export CFLAGS CPPFLAGS CXXFLAGS LDFLAGS
 
+NUMJOBS := -j$(shell nproc)
+
 # Uncomment this to turn on verbose mode.
 #export DH_VERBOSE=1
 
 	# Add here command to compile/build the package.
 	# Build first things.
 	# Build Xvnc
-	make LDFLAGS="-lpng"
-	(cd unix/xserver;make)
+	make $(NUMJOBS) LDFLAGS="-lpng"
+	make $(NUMJOBS) -C unix/xserver
 
 	touch build-arch-stamp