Allow disabling fcntl (and use softfilelock) with environment variable

[leoleoasd]

I'm using a cluster and the home directory is a network volume that has fcntl disabled.

filelock/src/filelock/_unix.py

Lines 25 to 31 in 481daa4

	else: # pragma: win32 no cover
	try:
	import fcntl
	except ImportError:
	pass
	else:
	has_fcntl = True

filelock currently selects fcntl whenever the library is available, ignoring its availability on the file system.

NotImplementedError: FileSystem does not appear to support flock; user SoftFileLock instead

Adding an environment or some other way to control this behavior would be better.

[yulonghui]

Hi~, @leoleoasd
I also met this problem, Do you know how to solve this problem, or how can I use SoftFileLock instead of FileLock in the system?
Thanks!

[leoleoasd]

import filelock
filelock.FileLock = filelock.SoftFileLock

import other_thing_requires_filelock