build: replace verstion extraction via set to use python

The version of roundup was extracted from roundup/__init__.py by sed.
It is used to label the roundup.pot template file.

Replaced the sed setup by importing roundup and printing the
__Version__ variable. This should be less fragile to spacing and other
changes.

Author: rouilj

locale/Makefile

@@ -83,8 +83,8 @@ roundup.pot: $(SOURCES) $(TEMPLATES)
 	  ../share/roundup/templates/devel/html/*.html \
 	  ../share/roundup/templates/minimal/html/*.html \
 	  ../share/roundup/templates/responsive/html/*.html
-	VERSION="`sed -ne \"/__version__/s/.*'\(.*\)'.*/\1/p\" \
-	      ../roundup/__init__.py`"; \
+	VERSION="`${RUN_PYTHON} -c 'from roundup import __version__; \
+	                            print(__version__)';`"; \
 	${XGETTEXT} -j -w 80 -F \
 	  --package-name=Roundup \
 	  --package-version=$$VERSION \