libmpd.cabal: don't build library when doing test build
libmpd.cabal: don't build library when doing test build

Avoid building the library twice when testing.

darcs-hash:20090118111613-928c4-f8e949dc8bb37b11ee24fb0d31bcb5ab518a9e5a.gz

sol/libmpd-haskell,beni55/libmpd-haskell