patch 9.1.1768: Makefile does not uninstall global plugins

Problem:  Makefile does not uninstall global plugins
          (after v9.1.1757)
Solution: Uninstall global plugins before installing them,
          so that old files are not carried around and loaded
          when no longer used.

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/Makefile

@@ -2474,7 +2474,8 @@ installrtbase: $(HELPSOURCE)/vim.1 $(DEST_VIM) $(VIMTARGET) $(DEST_RT) \
 # install the standard import files
 	cd $(IMPORTSOURCE)/dist; $(INSTALL_DATA) *.vim $(DEST_IMPORT)/dist
 	cd $(DEST_IMPORT)/dist; chmod $(HELPMOD) *.vim
-# install the standard plugin files
+# install the standard plugin files, but first remove existing ones
+	-rm -f $(DEST_PLUG)/*.vim
 	cd $(PLUGSOURCE); $(INSTALL_DATA) *.vim README.txt $(DEST_PLUG)
 	cd $(DEST_PLUG); chmod $(HELPMOD) *.vim README.txt
 # install the ftplugin files

src/version.c

@@ -724,6 +724,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1768,
 /**/
     1767,
 /**/