Merge branch 'maint' (with edits) test defs: define default $distdir (help reducing duplication) * tests/defs ($distdir): New variable, might be used in testcases checking distribution-related features. * tests/pr9.test: Use it. * tests/subdir9.test: Likewise. * tests/lex3.test: Likewise. * tests/lexvpath.test: Likewise. * tests/remake-moved-m4-file.test: Likewise. * tests/remake-renamed-m4-file.test: Likewise. * tests/remake-renamed-m4-macro-and-file.test: Likewise. * tests/yacc-basic.test: Likewise. * tests/yacc-d-basic.test: Likewise. * tests/yacc-d-vpath.test: Likewise. * tests/yacc-dist-nobuild.test: Likewise. * tests/vtexi3.test: Add comment explaining why we redefine $distdir in this test.