isComposing (RFC3994) parser and generator

darcs-hash:20091112171006-56b4d-2d106f35effe451271c9c2a929a19b35258dc610
Set correct cflags when compiling on Snow Leopard

Ignore-this: cdf0e7dcb3c29edba691e33978e78444

darcs-hash:20091112092640-56b4d-6df737a2884bbf8e6a305e1b51cd52302e1250d9