Using wx to prevent concurrent writes to the cache

[martinheidegger]

@loklaan kindly provided #5 as an attempt to prevent to deal with the issue presented in #3. When reviewing it and writing a test I thought that using wx as a file mode might be more efficient - as it works even though not the same node instance is trying to access the same cache - and results in less lines of code.

[coveralls]

Coverage remained the same at 98.039% when pulling 671b81f on fix-write-lock-safety2 into 4df22ef on master.

[loklaan]

Oh yeah, this totally makes sense! I'll close #5

Thanks for jumping on this so quick, and successfully making a test too

[martinheidegger]

Published as 1.2.2

[loklaan]

Yaaas, thanks!