Insist on a space after a mnemonic with -w

[Homo-carbonis]

I'm not that good with git but I think I managed to do the rebase properly this time. The update to streampos is now gone.

[mungre]

Thank you, that looks good.

(Discussed in #80)

[chriskillpack]

@mungre merge this if you think this should go into v1.10.

[mungre]

I'm not sure about this one for v1.10. It is a good idea but it's also a breaking change potentially.

@ZornsLemma what do you think?

[ZornsLemma]

I agree, it's probably best to keep this out of 1.10. It is a good idea (assuming there isn't a lurking gotcha where calculated values that "should" fail in practice start to work because they generate a negative value) but there's a fair risk of breaking something, and this is a long-standing behaviour so I don't think we should rush to change it with a release so close.

[mungre]

I merged this into master manually since we're no longer using proposed-updates.