decrypt_file() with output=<file with spaces> results in usage error

[alexvh]

Using decrypt_file() with an output argument that includes spaces results in a usage error from gpg on Linux. Each string separated by spaces is passed as an argument to gpg rather than the string as a whole in quotes.

Attached is a quick and dirty patch that fixes the issue on Linux at least. I'm certain it's incomplete and probably buggy, but including here for reference.

gnupg.txt

[isislovecruft]

There's code review started for the patch in PR #136, which needs only very minor revision to add a comment about what a regex is supposed to do.