Add localization to calcurse-upgrade

* Use gettext in "scripts/calcurse-upgrade".

* Add "scripts/calcurse-upgrade" to "po/POTFILES.in".

* Rename "scripts/calcurse-upgrade" to "scripts/calcurse-upgrade.sh" to
  make sure xgettext(1) detects the correct input file format.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

scripts/Makefile.am

@@ -1,3 +1,13 @@
 AUTOMAKE_OPTIONS = foreign
 
-dist_bin_SCRIPTS = calcurse-upgrade
+dist_bin_SCRIPTS = \
+	calcurse-upgrade
+
+EXTRA_DIST = \
+	calcurse-upgrade.sh
+
+CLEANFILES = \
+	calcurse-upgrade
+
+calcurse-upgrade: calcurse-upgrade.sh
+	$(AM_V_GEN) $(INSTALL) $< $@