Use pkgconfig-depends for fuse dependency

This fixes a compilation problem on OS X, since here at least the fuse
library is known as osxfuse instead of fuse. Should work reliably on
other platforms as well thanks to the cross-platform nature of
pkg-config.

Also remove fuse.h from global includes list; this was causing
compilation failure on OS X due to not having a FUSE_USE_VERSION defined
previously.