Properly ignore files in build-aux directory

We want to ignore all files except *.pl in build-aux directory, however
the unignore pattern "!/build-aux/*.pl" doesn't have any effect because
a previous "/build-aux/" pattern ignores the directory itself rather
than individual files in it.

https://bugzilla.redhat.com/show_bug.cgi?id=1439994Signed-off-by: NJiri Denemark <jdenemar@redhat.com>
(cherry picked from commit f0ad8e7e)

.gitignore

@@ -43,7 +43,7 @@
 /NEWS
 /aclocal.m4
 /autom4te.cache
-/build-aux/
+/build-aux/*
 /build/
 /confdefs.h
 /config.cache