Calling _set_debug(True) doesn't import inspect

[zooba]

When the tests enable debug messages, they call this function and pass True:

psutil/psutil/__init__.py

Lines 2349 to 2355 in dd57b9a

	def _set_debug(value):
	"""Enable or disable PSUTIL_DEBUG option, which prints debugging
	messages to stderr.
	"""
	import psutil._common
	psutil._common.PSUTIL_DEBUG = bool(value)
	_psplatform.cext.set_debug(bool(value))

However, if the environment variable wasn't already set, the import of inspect was skipped and any attempt to display a debug message will fail.

psutil/psutil/_common.py

Lines 46 to 48 in dd57b9a

	PSUTIL_DEBUG = bool(os.getenv('PSUTIL_DEBUG', 0))
	if PSUTIL_DEBUG:
	import inspect

The import of inspect should probably just be done inside the debug function.