Configure test for libxml2 always succeeds

[HansWeltar]

How to reproduce:

• Do not install libxml2
• (might want to make sure /bin/sh is not symlinked to bash)
• run ./configure

checking for python module libxml2... found
checking that generated files are newer than configure... Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'libxml2'
done
configure: creating ./config.status
config.status: creating Makefile
config.status: creating itstool
config.status: creating itstool.1
config.status: creating its/Makefile
config.status: creating setup.py

As you can see, configure falsely claims it found libxml2 even though it's absent.
The next error is ignored.
The rest of the build proceeds with success, but itstool fails to run giving an import error on libxml2.

root cause:
bash versus sh semantics for &>.
The line to test for libxml2 is the following: echo "import $py_module" | $PYTHON - &>/dev/null
Then the exit-code $? is checked for success.

In bash &> is shorthand for redirect stdout +stderr
/bin/sh interprets &> as & (run in background) > (redirect output)
When running in background the exit-code is always 0 (success) and thus the test for libxml2 always succeeds

./configure explicitly states #!/bin/sh in the shebang so /bin/sh semantics should be observed.

Fix:
replace &>/dev/null with >/dev/null 2>&1 in ./configure
This expression is valid for both bash and sh.
patch_itstool_libxml2_detect.txt

[shaunix]

Today I learned a bashism I was unaware of. Thanks. I think I'm going to switch entirely to setuptools for the next version, which will make this issue go away. But I'll keep this issue open for now.