Fix @ code blocks

In cases where we had some horizontal space before the closing ‘@’, the
parser would not accept the block as a code block and we'd get ugly
output.
Update tests

This updates tests due to Haddock Trac #271 fix and due to removal of
TypeHoles as an extension from GHC.
Revert "Support for -XPatternSynonyms"

This reverts commit 7c905816eb12981840efe4136989799db437f357.

This commit broke tests in at least two ways:

* added spurious whitespace to the front of each function name (not user
  visible)

* made all infix data types now be parenthesised (very user visible)

While the first one is easily fixable, I don't know about the second
one. I dare not try because the commit in question added no tests about
the added feature so it's impossible to tell what we're breaking.