[issue15955] gzip, bz2, lzma: add option to limit output size

[Martin Panter]

Martin Panter added the comment:

Here is a patch for the higher-level LZMAFile implementation to use Nikolaus’s “max_length” parameter. It depends on Nikolaus’s patch also being applied.

I split out a _RawReader class that does the actual decompress() calls, and then wrapped that in a BufferedReader. This avoids needing any special code to implement buffering, readline(), etc. The only significant changes in the API that I can see are:

* LZMAFile now inherits the useless specification of BufferedReader.peek(), losing the guarantee of returning at least a single byte. I questioned the BufferedReader specification at <https://bugs.python.org/issue5811#msg233750>.
* read() now accepts size=None, because BufferedReader does. I had to change a test case for this.

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Added file: http://bugs.python.org/file37658/LZMAFile.patch

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