Add writeToByteString

This function is useful when you want to efficiently construct
a short fixed-sized bytestring.
Merge pull request #11 from takano-akio/write-to-byte-string

Add a function that directly converts a Write to a ByteString
Merge branch 'master' into compat

Conflicts:
	Blaze/ByteString/Builder.hs
	Blaze/ByteString/Builder/Internal.hs
Fix Setup.hs to not preempt error messages

For example,  if dependencies are missing, the old Setup.hs would
return "error detecting bytestring version" instead of the correct
"missing text".
Make Setup.hs compatible with Cabal 1.8 (GHC 6.12)

Making Setup.hs compatible with Cabal 1.6 is not easy, because
isSpecificVersion is not available. That would seem to imply that
that Setup.hs would need to refer to the ThisVersion constructor
directly, which is now deprecated.

And, I haven't found a way to use CPP to make Setup.hs that compiles
correctly across a wider versions of Cabal.
Make Html.Utf8 compile with GHC 7.2 and earlier