"main-is" misparsed in if/else, only by sdist

(Imported from [Trac #817](http://hackage.haskell.org/trac/hackage/ticket/817), reported by @jeffwheeler on 2011-03-22)

An if/else block which sets the main-is value for an executable based on a flag is misparsed when running "cabal sdist" (it's parsed correctly when running "cabal install").

Upon failure, it appears that it's looking for a filename that is the two main-is options concatenated together. E.g., I get the error "cabal: `HackerMain?`.hsMain.hs doesn't exist".

The problematic bit looks like:

if flag(hacking)

main-is: `HackerMain?`.hs

else

main-is: Main.hs

My entire config can be found on hpaste: [http://hpaste.org/44939/yicabal](http://hpaste.org/44939/yicabal) (problematic lines around 268).