Don't expand empty [paths] so later interpolation can do the right thing.
Example:
[paths]
default =
default-push = %(default)s
#!/bin/sh
hg init
touch a.o
touch a.c
touch syntax
mkdir dir
touch dir/a.o
touch dir/b.o
touch dir/c.o
hg add dir/a.o
hg commit -m 0
hg add dir/b.o
echo "--" ; hg status
echo "*.o" > .hgignore
echo "--" ; hg status
echo ".*\.o" > .hgignore
echo "--" ; hg status
# XXX: broken
#echo "glob:**.o" > .hgignore
#echo "--" ; hg status
#
#echo "glob:*.o" > .hgignore
#echo "--" ; hg status
echo "syntax: invalid" > .hgignore
echo "--" ; hg status
echo "syntax: glob" > .hgignore
echo "*.o" >> .hgignore
echo "--" ; hg status
echo "relglob:syntax*" > .hgignore
echo "--" ; hg status
echo "relglob:*" > .hgignore
echo "--" ; hg status
cd dir
echo "--" ; hg status .