templater: teach template loader to use open_template() function
The template loader can apparently load templates from relative paths,
so I needed to add that support to `open_template()`.
This takes the number of failing tests with PyOxidizer from 54 to 34.
Differential Revision: https://phab.mercurial-scm.org/D8907
#require rust
$ rhg() {
> if [ -f "$RUNTESTDIR/../rust/target/debug/rhg" ]; then
> "$RUNTESTDIR/../rust/target/debug/rhg" "$@"
> else
> echo "skipped: Cannot find rhg. Try to run cargo build in rust/rhg."
> exit 80
> fi
> }
$ rhg unimplemented-command
[252]
$ rhg root
abort: no repository found in '$TESTTMP' (.hg not found)!
[255]
$ hg init repository
$ cd repository
$ rhg root
$TESTTMP/repository
$ rhg root > /dev/full
abort: No space left on device (os error 28)
[255]
$ rm -rf `pwd`
$ rhg root
abort: error getting current working directory: $ENOENT$
[255]