[PATCH 4 of 5 STABLE] make: add forgotten hgext3rd to clean rule

[Sean Farley]

# HG changeset patch
# User Sean Farley <sean at farley.io>
# Date 1460746317 25200
#      Fri Apr 15 11:51:57 2016 -0700
# Branch stable
# Node ID 06027f4c174a930cbeb1d1d7b0b85a5990244f11
# Parent  8aca7fdddfbaeb1e7afd30cd2a0c24cb7b2ea80c
# EXP-Topic ppa
make: add forgotten hgext3rd to clean rule

diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -57,11 +57,11 @@ wheel:
 doc:
 	$(MAKE) -C doc
 
 clean:
 	-$(PYTHON) setup.py clean --all # ignore errors from this command
-	find contrib doc hgext i18n mercurial tests \
+	find contrib doc hgext hgext3rd i18n mercurial tests \
 		\( -name '*.py[cdo]' -o -name '*.so' \) -exec rm -f '{}' ';'
 	rm -f $(addprefix mercurial/,$(notdir $(wildcard mercurial/pure/[a-z]*.py)))
 	rm -f MANIFEST MANIFEST.in hgext/__index__.py tests/*.err
 	if test -d .hg; then rm -f mercurial/__version__.py; fi
 	rm -rf build mercurial/locale