validate i18n strings when running "make lint"

* Add bootstrap-autogen depdenency to lint target to force
  generated files to be created.

* Add validate-src-strings to lint rules

* Add validate-src-strings as dependency to lint targett

* Remove obsolete test_lang frm test target

* Add diagnostic message to validation command in i18n.py
  that outputs how many objects were scanned. Formerly it only
  output a message if there were errors. This made it impossible to
  distinguish an empty file from one with no errors.

* While adding the validation counts it was discovered plurals had
  been omitted for some of the validation checks. Added the missing
  checks for plural forms.

* Also distinguished between errors and warnings. Permit warnings to
  be emitted but do not fail the validatition unless actual errors
  were also detected.

install/po/Makefile.in

@@ -160,7 +160,7 @@ install: $(mo_files)
 	done
 
 mostlyclean:
-	rm -rf *.mo test.po test_locale
+	rm -rf *.mo test.po test_locale tmp.pot
 	rm -f $(DOMAIN).pot.update $(DOMAIN).pot.update.tmp $(DOMAIN).pot.tmp
 
 clean: mostlyclean
@@ -179,6 +179,14 @@ validate-pot:
 validate-po:
 	$(IPA_TEST_I18N) --show-strings --validate-po $(po_files)
 
+validate-src-strings:
+	@rm -f tmp.pot
+	@touch tmp.pot
+	@$(MAKE) DOMAIN=tmp update-pot; \
+	status=$$?; \
+	rm tmp.pot; \
+	exit $$status
+
 debug:
 	@echo Python potfiles:
 	@echo PY_FILES = $(PY_FILES)