hgdemandimport: disable on Python 3.5
The demand importer functionality isn't working at all on Python 3.5.
I'm not sure what's wrong.
Since it isn't working, let's disable it completely.
```
$ HGRCPATH= hyperfine -w 1 -r 50 -- "~/.pyenv/versions/3.5.9/bin/python ./hg version" \
"HGDEMANDIMPORT=disable ~/.pyenv/versions/3.5.9/bin/python ./hg version"
Benchmark #1: ~/.pyenv/versions/3.5.9/bin/python ./hg version
Time (mean ± σ): 163.7 ms ± 2.2 ms [User: 148.5 ms, System: 15.7 ms]
Range (min … max): 161.0 ms … 170.2 ms 50 runs
Benchmark #2: HGDEMANDIMPORT=disable ~/.pyenv/versions/3.5.9/bin/python ./hg version
Time (mean ± σ): 164.3 ms ± 1.4 ms [User: 148.2 ms, System: 16.6 ms]
Range (min … max): 161.4 ms … 169.8 ms 50 runs
```
Differential Revision: https://phab.mercurial-scm.org/D7953
$ hg init outer
$ cd outer
$ echo '[paths]' >> .hg/hgrc
$ echo 'default = http://example.net/' >> .hg/hgrc
hg debugsub with no remapping
$ echo 'sub = libfoo' > .hgsub
$ hg add .hgsub
$ hg debugsub
path sub
source libfoo
revision
hg debugsub with remapping
$ echo '[subpaths]' >> .hg/hgrc
$ printf 'http://example.net/lib(.*) = C:\\libs\\\\1-lib\\\n' >> .hg/hgrc
$ hg debugsub
path sub
source C:\libs\foo-lib\
revision
test cumulative remapping, the $HGRCPATH file is loaded first
$ echo '[subpaths]' >> $HGRCPATH
$ echo 'libfoo = libbar' >> $HGRCPATH
$ hg debugsub
path sub
source C:\libs\bar-lib\
revision
test absolute source path -- testing with a URL is important since
standard os.path.join wont treat that as an absolute path
$ echo 'abs = http://example.net/abs' > .hgsub
$ hg debugsub
path abs
source http://example.net/abs
revision
$ echo 'abs = /abs' > .hgsub
$ hg debugsub
path abs
source /abs
revision
test bad subpaths pattern
$ cat > .hg/hgrc <<EOF
> [subpaths]
> .* = \1
> EOF
$ hg debugsub
abort: bad subrepository pattern in $TESTTMP/outer/.hg/hgrc:2: invalid group reference* (glob)
[255]
$ cd ..